j 


I  February  1"),  ]'.)12. 


U.  S.  DEPARTMF.NT  OF  AGRICULTURE, 

BUREAU  OF  ANIMAL  INDUSTRY.—  BULLETIN  143- 


A.  D.  MHLVIN,  CHIEF  OF  BUREAU. 


THE  MAIXTKXAXCE  RATIONS  OF 
FARM 


HENRY  PRENTISS  ARMSBY,  Pn.  I).,  LL.  I)., 

r  of  the  Institute  of  Animal  Xutrition  of  The  Pennsylvania 
State  College;  E.rpert  in  Animal  Nutrition, 
Bureau  of  Animal  Industry. 


WASHINGTON: 

GOVERNMENT   PRINTING   OFFICE. 
1912. 


Issued  February  15,  1912. 

U.  S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU  OF  ANIMAL  INDUSTRY.— BULLETIN  143. 

A.  D.  MELVIN,  CHIEF  OF  BUREAU. 


THE  MAINTENANCE  RATIONS  OF 
FARM  ANIMALS. 


BY 


HENRY  PRENTISS  ARMSBY,  PH.  D.,  LL.  D., 

Director  of  the  Institute  of  Animal  Nutrition  of  The  Pennsylvania 

State  College;  Expert  in  Animal  Nutrition, 

Bureau  of  Animal  Industry. 


WASHINGTON: 
GOVERNMENT   PRINTING   OFFICE. 

1912. 


THE  BUREAU  OF  ANIMAL  INDUSTRY. 


Chief:  A.  D.  MELVIX. 
Assistant  Chief:  A.  M.  FARRINCTON. 
Chief  Clerk:  CHARLES  C.  CARROLL. 

Animal  Husbandry  Division:  GEORGK  M.  ROMMEL,  chief. 
Biochcmic  Division:  M.  DORSET,  chief. 
Dairy  Division:  B.  H.  RAWL,  chief. 

Inspection  Division:  RICE  P.  STEDDOM,  chief;  MORRIS  WOODEN,  K.  A.  It  AM  SAY, 
and  ALBERT  E.  BEHNKE,  associate  chiefs. 

Pathological  Division:  JOHN  It.  MOHLEB,  chief. 
Quarantine  Division:  RICHARD  W.  HICKMAN,  chief. 
Zoological  Division:  B.  H.  RANSOM,  chief. 
Experiment  Station:  E.  C.  SCIIROEDER,  superintendent. 
Editor:  JAMES  M.  PICKENS. 
2 


LETTER  OF  TRANSMITTAL 


U.  S.  DEPARTMENT  OF  AGRICULTURE. 

BUREAU  OF  ANIMAL  INDUSTRY, 
Washington,  D.  C.,  August  12,  1911. 

SIR:  I  have  the  honor  to  transmit  herewith,  and  to  recommend  for 
publication  in  the  bulletin  series  of  this  bureau,  a  manuscript  entitled 
"  The  Maintenance  Rations  of  Farm  Animals,"  by  Dr.  Henry  Pren- 
tiss  Armsby,  who  has  charge  of  the  cooperative  work  in  animal 
nutrition  between  this  bureau  and  the  Institute  of  Animal  Xtitri- 
tion  of  The  Pennsylvania  State  College.  The  paper  is  based  not 
only  on  Dr.  Armsby's  own  work,  but  on  that  of  other  investigators 
as  well,  and  is  believed  to  cover  the  subject  thoroughly. 

Respectfully, 

A.  I).  MELVIN. 

Chief  of  Bureau. 
Hon.  JAMES  WILSON, 

Secretary  of  Agriculture. 


CONTENTS. 


Page. 

Introduction 7 

The  fasting  katabolism 8 

Purpose  of  the  fasting  katabolism 9 

The  material  katabolized 10 

Ash 10 

Fal 10 

Carbohydrates 10 

Protein II 

Ratio  of  protein  to  total  katabolism II 

Influence  of  body  fat 12 

Influence  of  surplus  protein 1 15 

Relative  constancy  of  energy  katabolism 13 

The  energy  requirement  for  maintenance 10 

Replacement  of  nutrients 10 

Feed  fat  and  body  fat 10 

Carbohydrates  and  body  fat 17 

Carbohydrates  and  feed  fat 17 

Feed  protein  and  body  fat 17 

Fat  or  carbohydrates  and  protein 18 

Availability  of  energy... 19 

Availability  for  cattle 20 

Availability  for  the  horse — Zuntz  and  Hagemann's  results 22 

Digestive  work  for  crude  fiber 23 

Work  of  mastication 23 

Computation  of  available  energy 24 

Availability  for  the  horse — Wolff's  results 25 

Availability  for  carnivora 26 

Causes  of  increased  metabolism 28 

Mechanical  work 29 

Secretion 29 

Fermentation 29 

Digestive  cleavages 30 

Intermediary  metabolism 31 

Excretion 32 

The  maintenance  ration 33 

Relation  of  maintenance  requirement  to  live  weight 30 

Computation  of  relative  body  smface 38 

The  maintenance  rations  of  farm  animals 39 

Cattle 39 

Sheep 48 

Swine 51 

The  horse 55 

Zuntz  and  Ilagemann's  investigations 55 

Wolff's  investigations 57 

Miintz's  experiments 02 

Grandeau  and  Le  Clerc's  results 02 

True  maintenance  and  live- weight  maintenance 0 


6  CONTENTS. 

Page. 

Factors  affecting  the  energy  requirement 64 

Muscular  activity 65 

Minor  muscular  motions 65 

Lying  and  standing 66 

Individuality 66 

Condition G7 

Age 68 

External  temperature 69 

Regulation  of  body  temperature 69 

Critical  temperature 71 

Feed  consumption  a  source  of  heat 71 

Isodynamic  replacement 72 

Relation  of  maintenance  ration  to  critical  temperature 72 

Feed  consumption  lowers  the  critical  temperature 73 

Critical  temperature  for  farm  animals 73 

The  protein  requirement  for  maintenance 74 

Protein  katabolized  during  fasting 74 

Influence  of  previous  feed 74 

Fasting  katabolism  variable 74 

The  minimum  of  protein 75 

Influence  of  nonnitrogenous  materials 76 

Relation  to  fasting  katabolism 76 

Effect  of  surplus  of  protein 78 

Increases  protein  katabolism 78 

Utilization  of  protein  limited 80 

Protein  as  a  source  of  energy 81 

Storage  of  protein 82 

Fluctuations  in  body  protein 83 

Relation  to  energy  supply 84 

Value  of  nonprotein 88 

Minimum   of  protein  for  farm  animals 89 

Cattle 89 

Sheep 94 

Swine 96 

The  horse 97 

The  optimum  of  protein 97 

Relative  values  of  proteins 99 

Differences  in  constitution  of  proteins 99 

Absence  of  certain  constituents 100 

Proport  ions  of  constituents 101 

Experimental  methods 102 

Michaud's  invest  igations 102 

Zisterer's  experiments 104 

Results  are  qualitative 105 

Thomas's  experiments 106 

Significance  of  results. . .                            108 


LLUSTRATION. 


Page. 
Fir.uRK  1 .     Availability  of  metabolizable  energy  of  hay 35 


1HE  MAINTENANCE  RATIONS  OF  FARM  ANIMALS. 


INTRODUCTION. 

Feed  is  supplied  to  farm  animals  in  order  that  they  may  either 
yield  products  useful  to  man  as  materials  for  human  food  and  cloth- 
ing or  serve  him  by  the  performance  of  mechanical  work.  But 
as  a  factory  must  first  be  supplied  with  enough  power  to  keep  in 
motion  the  shafting,  belting,  and  other  machinery  before  any  product 
can  be  turned  out,  so  the  animal  mechanism  must  be  provided  with 
sufficient  feed  to  maintain  the  processes  essential  to  life  before  any 
continued  production  is  possible.  The  amount  of  feed  required  for 
this  purpose  is  called  the  maintenance  ration  of  the  particular  animal. 
It  is  the  quantity  of  feed  necessary  simply  to  support  the  animal 
when  doing  no  work  and  yielding  no  material  product.  If  an  animal 
receiving  exactly  a  maintenance  ration  were  subjected  to  a  so-called 
balance  experiment,  there  would  be  found  an  exact  equality  between 
income  and  outgo  of  ash,  nitrogen,  carbon,  hydrogen,  and  energy, 
showing  that  the  body  was  neither  gaining  nor  losing  protein,  fat, 
carbohydrates,  or  ash. 

The  word  "maintenance"  is  sometimes  used  popularly  in  another 
sense  to  signify  the  total  amount  of  feed  required,  for  example,  by  a 
horse  in  order  to  perform  his  daily  work  or  by  a  calf  in  order  to  make 
a  normal  growth.  It  is  important  to  grasp  the  idea  that,  in  its 
technical  sense,  the  maintenance  requirement  means  the  minimum 
required  simply  to  sustain  life.  The  feed  of  the  horse  or  calf  would, 
from  this  point  of  view,  be  regarded  as  consisting  of  two  portions; 
one  of  these  is  the  maintenance  ration,  which  if  fed  by  itself  would 
just  support  the  horse  at  rest  or  the  calf  without  growth,  and  the 
other  the  productive  portion  of  the  ration  by  means  of  which  work 
is  done  or  growth  made.  To  recur  to  the  illustration  of  the  factory, 
the  maintenance  ration  keeps  the  empty  machinery  running,  while 
the  additional  feed  furnishes  the  power  necessary  to  turn  out  the 
product. 

It  might  seem  at  first  thought  that  not  much  importance  attaches 
to  a  study  of  the  maintenance  ration.  The  animal  kept  on  such 
a  ration  yields  no  direct  economic  return  and  hence  simple  main- 
tenance feeding  should  be  avoided,  so  far  as  practicable,  and  when 

7 


8  MAINTENANCE  RATIONS   OP   FARM   ANIMALS. 

it  appears  desirable  to  practice  it  the  observation  of  the  skilled 
stockman,  especially  if  supplemented  by  occasional  weighings,  will 
usually  suffice  to  determine  whether  or  not  the  end  is  being  attained. 
Nevertheless,  the  subject  has  significance  for  practice  as  well  as  for 
science.  A  very  considerable  fraction  of  the  feed  actually  con- 
sumed by  farm  animals — on  the  average  probably  fully  one-half— 
is  applied  simply  to  maintenance.  But  if  half  of  the  farmer's  feed 
bill  is  expended  for  maintenance,  it  is  clearly  important  for  him  to 
know  something  of  the  laws  of  maintenance — how  its  requirements 
vary  as  between  different  animals,  how  they  are  affected  by  the  con- 
ditions under  which  animals  are  kept,  how  different  feeding  stuffs 
compare  in  value,  etc. — as  well  as  to  understand  the  principles  gov- 
erning the  production  of  meat,  milk,  or  work  from  the  other  half  of 
his  feed. 

Physiologically,  too,  the  maintenance  requirement  represents  the 
demand  of  the  basal  life  processes.  The  prime  necessity  of  the  organ- 
ism is  to  maintain  itself.  It  must  live  before  it  can  grow  or  propagate 
its  kind,  and  in  the  phenomena  of  maintenance  the  fundamental 
processes  of  nutrition  may  be  studied  uncomplicated  by  the  demands 
of  growth,  fattening,  or  reproduction. 

THE   FASTING   KATABOLISM.1 

Unlike  the  operations  of  a  factory,  which  cease  when  the  power  is 
shut  off,  the  activities  of  the  animal  do  not  stop  when  food  is  with- 
drawn, but  continue  for  a  variable  length  of  time  at  the  expense  of 
the  materials  of  the  body.  It  is  as  if  the  materials  of  the  factory 
itself  were  being  cut  up  and  used  for  fuel  under  the  boilers.  Men  have 
fasted  voluntarily  for  30  days  or  more  without  obvious  permanent  ill 
effects,  and  there  are  records  of  dogs  having  survived  fasting  periods 
of  from  90  to  100  or  more  days.  In  the  fasting  animal  at  rest  the  vital 
activities  are  reduced,  as  it  were,  to  their  simplest  terms,  practically 
only  those  functions  being  active  which  are  essential  to  continued  life. 
The  following  approximate  estimate  by  Zuntz  of  the  factors  of  the 
kitabolism  of  a  fasting  man  may  serve  to  give  a  general  idea  of  their 
nature  and  relative  importance.  The  figures  show  the  oxygen  con- 
sumption per  minute  of  the  various  tissues  and  its  percentage  distri- 
bution : 

1  For  references  to  the  literature  of  the  fasting  katabolism  compare: 

Ma  WHIN  Levy.  Von  Noorden's  Pathologic  lies  StofTwcchsels,  I'd  ed..  T.  L'L'L'-lilTi  and 
.",10-?,  15. 

Tigerstedt.      Nagel's  Ilandlnich  der  Physiologic  des  Mensohen,  I,  .".Tfi-nOI. 

Lusk.     The  Science  of  Nutrition.     2d  ed.,  .r»4-85. 

Henedict.  Metabolism  in  Inanition.  Carnegie  Institution  of  Washington.  Publication 
No.  77,  II,  36 1-304. 

Armsby.     Principles  of  Animal  Nutrition.  .°,d  ed.,  80-92  and  340-347. 


THE   FASTING   KATABOLISM. 


Consumption  of  oxygen  in  fasting  man  weighing  10  kilograms — Kuntz. 


Cubic 
centimeters 
per  minute. 

Percentage. 

Circulation  and  respiration                                                      .           .  .        .... 

30.0 

12.45 

Voluntary  muscles                                                        

112.0 

40.49 

Glands  and  other  organs: 

45.  0 

18.68 

Small  intestine                            

25.1 

10.42 

Kidneys  

10.5 

4.36 

Pancreas                                              ....          

9.3 

3.86 

Large  intestine              

7.0 

2.91 

Salivary  glands  

2.0 

.83 

9S  9 

Total                                                                  .             

240.9 

100.00 

According  to  the  foregoing  table  nearly  00  per  cent  of  the  metab- 
olism of  a  fasting  man  is  due  to  the  work  of  the  muscles,  including 
that  of  respiration  and  circulation  as  well  as  the  limited  activity  of 
the  voluntary  muscles,  while  somewhat  over  40  per  cent  is  due  to  the 
internal  organs.  Xo  equally  complete  data  are  available  for  farm 
animals,  but  the  supposition  seems  justified  that  their  metabolism 
in  its  main  features  is  not  greatly  unlike  that  of  man.  It  may  be 
noted  that  Zuntz  and  Hagemann  found  the  energy  expended  in 
respiration  and  circulation  by  the  horse  in  a  state  of  rest  to  be,  re- 
spectively, 4.7  and  5.01  per  cent  of  the  total  metabolism.  The  sum 
of  these — 0.71  per  cent — is  approximately  comparable  with  the  cor- 
responding figure  for  man. 

PURPOSE  OF  THE  FASTING  KATABOLISM. 

The  animal  body  is  primarily  a  transformer  of  energy.  From  the 
biochemical  standpoint  the  essential  phenomenon  of  physical  life 
is  the  transformation  of  chemical  into  kinetic  energy  which  accom- 
panies the  breaking  down  of  more  or  less  complex  molecules  into 
simpler  ones,  and  all  vital  activities  are  essentially  manifestations  of 
energy.  In  the  fasting  state  this  energy  is  derived  from  the  store 
of  chemical  energy  contained  in  the  materials  of  the  body  itself. 
The  very  act  of  living,  in  the  foregoing  view  of  it,  is  synonymous 
with  the  expenditure  by  the  organism  of  its  stored-up  capital  of 
energy.  The  prime  and  dominating  purpose  of  the  fasting  katab- 
olism.  therefore,  is  to  supply  energy  for  the  life  actions. 

But  since  the  necessary  activities  of  the  fasting  organism  are  car- 
ried on  by  means  of  energy  derived  from  the  katabolism  of  materials 
contained  in  the  tissues,  the  body's  store  of  matter  and  of  energy  is 
being  constantly  depleted.  To  prevent  or  replace  this  loss  will  re- 
quire a  corresponding  supply  of  available  material  and  energy  in  the 
feed.  A  knowledge  of  the  kind  and  quantity  of  material  katabolized 
during  fasting  and  of  the  amount  of  energy  liberated,  therefore,  is 
obviously  the  first  step  toward  ascertaining  the  supply  necessary  in 
the  feed. 


10  MAINTENANCE   RATIONS   OF   FARM   ANIMALS. 

THE    MATERIAL    KATABOLIZED. 

Ash. — The  fasting  organism  suffers  a  continual  loss  of  the  so-called 
ash  ingredients  of  its  tissues,  including  both  the  sulphur  and  phos- 
phorus of  its  proteins  and  the  more  distinctly  "mineral"  elements, 
such  as  sodium,  potassium,  calcium,  magnesium,  chlorin,  etc.  These 
elements  are  just  as  essential  to  the  existence  of  the  animal  as  are 
the  carbon,  nitrogen,  hydrogen,  and  oxygen  of  the  so-called  "  or- 
ganic "  compounds. 

The  study  of  this  branch  of  the  subject,  however,  has  hardly  pro- 
gressed far  enough  as  yet  to  permit  a  definite  formulation  of  the  ash 
requirements  of  domestic  animals.  The  present  paper,  therefore,  will 
be  confined  to  a  discussion  of  the  maintenance  requirements  in  the 
more  limited  and  customary  sense,  including  only  those  substances 
whose  function  it  is  wholly  or  in  part  to  serve  as  sources  of  energy. 

Fat. — It  is  a  familiar  conception  that  fat  formation  is  the  body's 
method  of  disposing  of  surplus  feed,  and  that  the  body  fat  is  a 
store  of  reserve  fuel  material.  The  converse  of  this  fact  is  equally 
familiar.  The  fasting  or  insufficiently  fed  animal  loses  fat  and  may 
reach  a  stage  of  extreme  emaciation  before  the  active  tissues  fail 
to  perform  their  duties.  Obviously,  the  fasting  animal  lives  very 
largely  upon  its  reserve  fat.  These  conclusions  from  common  obser- 
vation have  been  fully  confirmed  by  comparative  analyses  of  the 
carcasses  of  well-fed  and  of  fasted  animals  as  well  as  by  the  results 
of  balance  experiments  in  which  the  exact  nature  of  the  outgo  from 
the  body  has  been  determined. 

Carbohydrates. — In  addition  to  fat,  the  body  stores  up  more  or 
less  nonnitrogenous  matter  in  the  form  of  glycogen  in  the  liver  and 
muscles.  During  the  first  few  days  of  fasting  this  store  of  carbo- 
hydrates is  also  drawn  upon,  as  is  indicated  by  the  fact  that  the 
respiratory  quotient  tends  to  approach  unity,  while  later  the  amount 
katabolized  becomes  very  small.  This  is  well  illustrated  by  Bene- 
dict's l  experiments  upon  fasting  men.  The  average  results  of  a 
number  of  experiments  in  which  men  fasted  for  from  two  to  seven 
Consecutive  days  were  as  follows: 

kdtdliolhf'd   hi/  fdxtinf)  men — Benedict. 


Number 

^>ay.                                                        of  sub- 
jects. 

Per  kilo- 
Total.        ^ 

weight. 

First  dav                                                  14 

Grams.         Grams. 
110.0                1.69 

Second  day             -  1  3 

40.  3                  .  62 

Third  dav                                                           6 

21.8                  .36 

Fourth  dav                5 

23.  3                  .  40 

Fifth  dav  "                                                                                                                     "  1 

8.2                    14 

Sixth  day.                     1 

21.7                  .38 

Seventh  dav                                                                                         .                            1 

IS  7                  .33 

'The  Influence  of  Inanition  on  Metabolism.      I'arnpjrio  Institution  of  Washington.  D.  C., 
>07,    i>.    4(14. 
-Another  subject  showed  n  sliirht  gain  of  glvroiren. 


RATIO  OF  PROTEIN  TO  TOTAL  KATABOLTSM. 


11 


Protein. — Balance  experiments,  however,  while  confirming  the 
conclusion  that  the  loss  of  tissue  in  fasting  usually  consists  chiefly 
of  fat  together  with  some  carbohydrates,  show  that  there  is  also  a 
continual  breaking  down  of  body  protein  and  a  corresponding  ex- 
cretion of  urinary  nitrogen.  While  the  energy  supply  of  the  fasting 
animal  is  chiefly  derived  from  the  breaking  down  of  nonnitrogenous 
material,  the  functional  activity  of  the  tissues  necessarily  involves  the 
katabolism  of  a  certain  amount  of  protein. 

RATIO   OF  PROTEIN   TO  TOTAL    KATABOLISM. 

Qualitatively,  then,  the  katabolism  of  the  fasting  animal  is  substan- 
tially a  katabolism  of  fat  and  of  protein,  and  it  becomes  of  interest 
to  consider  the  quantitative  relations  between  the  two.  Such  a  com- 
parison is  best  made  on  the  basis  of  the  amounts  of  energy  liberated  in 
the  body  in  the  katabolism  of  protein  and  of  fat  respectively.  This 
aspect  of  the  subject  has  been  treated  especially  in  an  article  by  E. 
Voit  -  in  which  the  results  of  a  considerable  number  of  fasting  ex- 
periments are  compiled  and  discussed.  While  some  of  Voit's  com- 
putations are  based  on  estimates,  they  are  sufficiently  accurate  to 
outline  definitely  the  main  features  of  the  fasting  katabolism.  In- 
cluding only  experiments  on  animals  well  nourished  at  the  beginning, 
he  obtained  the  following  averages  for  the  percentage  of  the  total 
energy  liberated  which  was  supplied  by  the  katabolism  of  protein  in 
the  case  of  a  number  of  different  species.  The  results  of  the  first  day 
or  two  of  fasting  are  not  included  in  the  averages. 

lioii  of  cncr(/i/  ilcrircd  from   i>rotcin   in  fiixtini/ — /•>'.   To/7. 


Protein 

Kind  of  animal. 

Live 
weight. 

katabolism 
in  per  cent 
of  total 

katabolism  . 

Kilos. 

Per  cent. 

115.0 

7.3 

Man                            

C3.7 

15.6 

(        28.0 

13.2 

Dog                                                

{        18.7 

10.7 

1          7.2 

13.5 

Rabbit       

2.7 

16.5 

.0 

10.8 

3  3 

7.4 

Hen                                                  

2.1 

10.0 

While  both  the  total  and  protein  katabolism  naturally  showed  a 
wide  range  as  to  absolute  amount,  whether  per  head  or  per  unit  of 
live  weight,  the  ratio  of  protein  to  total  katabolism  proved  notably 
uniform  with  only  two  exceptions.  The  experiments  upon  dogs,  27 
in  number,  included  in  the  foregoing  table  furnished  the  basis  for 
the  following  comparison,  showing  that  in  74  per  cent  of  the  cases 
the  ratio  ranged  from  10  to  17  per  cent. 

1  Zeitselirift   fiir  Riolotjio,   vol.   41,   p.    107. 


12  MAINTENANCE   RATIONS   OF   FARM   ANIMALS. 

Protein  katabolism  of  dog  in  per  cent  of  total  kataboU&m-. 


Number  of  cases. 


Absolute.'  Percent. 


Less  than  10  per  cent  

4 

14.8 

10  to  14  per  cent 

15 

55  6 

14  to  17  per  cent  

18.5 

More  than  17  per  cent  .   .                                   .   .                   

3 

11.1 

27 

100.0 

It  may  be  accepted  as  established,  then,  that  in  what  may  be  spoken 
of  as  the  normal  fasting  animal,  in  which  the  influence  of  the  pre- 
vious feeding  has  disappeared  and  in  which,  on  the  other  hand,  the 
fat  reserve  has  not  been  exhausted,  the  protein  katabolism  constitutes 
a  fairly  small  percentage  of  the  total  katabolism,  both  being  ex- 
pressed in  terms  of  energy. 

INFLUENCE   OF   BODY   FAT. 

It  is  clear,  however,  from  the  foregoing  figures  that  the  ratio  of 
protein  to  total  katabolism  may  vary  considerably.  The  most  impor- 
tant factor  in  this  variation  has  been  found  to  be  the  relative  amount 
of  fat  contained  in  the  body.  So  long  as  fuel  material  in  the  form 
of  body  fat  is  readily  available,  the  amount  of  protein  katabolized 
remains  small.  Usually,  however,  the  store  of  fat  in  the  body  is  less 
than  that  of  protein,  while  in  fasting  its  exhaustion  is  relatively 
more  rapid.  There  comes  a  time,  therefore,  when  the  supply  of  non- 
nitrogenous  material  to  the  tissues  begins  to  flag.  When  this  hap- 
pens, the  protein  katabolism  begins  to  increase — that  is,  when  the 
supply  of  reserve  fuel  material  runs  low  the  organism  begins  to  use 
the  protein  of  its  own  tissues  as  a  source  of  energy,  and  E.  Voit l 
shows  that  this  occurs  whenever  the  ratio  of  fat  to  protein  remain- 
ing in  the  body  falls  below  a  certain  limit.  If  the  animal  was  origi- 
nally well  fed,  this  rise  in  the  protein  katabolism  occurs  only  shortly 
before  death,  from  which  fact  it  has  received  the  name  of  the  pre- 
mortal  rise.  In  the  case  of  very  fat  animals  this  point  may  never 
be  reached,  while,  on  the  other  hand,  in  a  lean  animal  the  protein 
katabolism  may  increase  steadily  from  the  very  beginning  of  the 
fasting.  The  following  three  experiments  upon  a  fat  guinea  pig,  a 
moderately  fat  dog,  and  a  lean  rabbit,  cited  by  Voit  from  Rubner's 
experiments,  may  serve  to  illustrate  these  three  types  of  fasting 
katabolism : 

1  Loc.  cit.,  p.  502. 


CONSTANCY   OF   ENEEGY   KATABOLISM. 
Proportion  of  energy  derived  from  protein — Rubner. 


13 


Guinea  pig. 

Dog. 

Rabbit. 

Day  of 
fasting. 

Protein  ka- 
ta  holism  in 
per  cent  of 
total  ka- 
tabolism. 

Day  of 
fasting. 

Protein  ka- 
ta  holism  in 
per  cent  of 
total  ka- 
tabolism. 

Day  of 
fasting. 

Protein  ka- 
ta  holism  in 
per  cent  of 
total  ka- 
tabolism. 

2 

Per  cent. 
10.4 
11.1 
11.0 
1,1.9 
11.8 
6.9 
11.2 
10.9 

2-4 

Per  cent. 
16.3 
13.1 
15.5 
17.4 
20.0 

3 

Per  cent. 
16.5 
23.6 
26.5 
29.8 
50.1 
96.4 

3 

10-11.... 

12  

5-7 

4 

9-12  
13-15.... 
16.. 

5 

13 

6  

7 

14. 

17-18.  .  .  . 

8      ..    . 

9  

INFLUENCE    OF    SURPLUS    PROTEIN. 


On  the  other  hand,  as  Pettenkofer  and  Voit  long  ago  showed,1 
when  an  animal  which  has  been  previously  receiving  large  amounts 
of  protein  is  deprived  of  feed,  the  high  protein  katabolism  which 
is  observed  during  the  first  two  or  three  days  of  fasting  is  accom- 
panied by  a  relatively  smaller  katabolism  of  fat.  Thus  in  an  experi- 
ment with  a  dog,  cited  on  a  subsequent  page  (p.  74)  to  illustrate 
the  initial  fall  of  protein  katabolism,  respiration  experiments  were 
made  on  the  second,  fifth,  and  eighth  days,  with  the  following 

results : 

Katabolism  of  fasting  doy — Vo-lt. 


Protein  ka- 

Day. 

Urinary 
nitrogen. 

Fat  ka- 
tabo- 
lized. 

tabolized  in 
;  per  cent  of 
total  ka- 

tabolism. 

Grams. 

Grams. 

j 

Second  day  

11.6 

86 

26.2 

Fifth  day  

5  7 

103 

12  7 

Eighth  day  

4.7 

99 

11.1 

1 

Obviously  we  have  here  the  reverse  of  what  takes  place  in  the  later 
days  of  fasting,  viz,  a  gradual  substitution  of  fat  for  protein  as  the 
readily  available  supply  of  the  latter  in  the  body  is  reduced.  Doubt- 
less the  effect  would  have  been  found  to  be  still  more  marked  on  the 
first  day  of  the  fasting,  when  the  protein  katabolism  was  equivalent 
to  28.1  grams  of  nitrogen. 

RELATIVE  CONSTANCY  OF  ENERGY   KATABOLISM. 

The  results  which  have  just  been  considered  regarding  the  nature 
of  the  material  katabolized  in  fasting  and  the  way  in  which  fat, 


1  Zeitschrift  fur  Biologie,  vol.  7,  p.  :569. 


14 


MAINTENANCE   RATIONS   OF   FARM  ANIMALS. 


carbohydrates,  and  protein  mutually  replace  each  other  as  fuel  ma- 
terial as  one  or  the  other  is  most  available  fully  substantiate  the 
assertion  made  on  page  0  that  the  controlling  factor  in  the  katabo- 
lism  of  the  fasting  body  is  the  demand  for  energy.  As  there  stated, 
the  body  is  essentially  a  converter  of  energy,  and  protein  occupies  a 
peculiar  position  in  nutrition  simply  so  far  as  it  is  a  part  of  the 
necessary  mechanism  for  this  conversion.  These  facts  can  hardly 
have  failed  to  suggest  that  the  demand  for  energy  must  be  relatively 
constant  in  the  same  individual,  and  that  such  is  in  fact  the  case  has 
been  demonstrated  by  a  large  number  of  experiments. 

For  example,  in  the  experiment  by  Voit  upon  a  dog,  just  cited,  the  energy  of 
the  protein  and  fat  katabolized  on  the  three  days,  as  computed  from  the  data 
for  the  urinary  nitrogen  and  for  the  fat  katabolism,  was  as  shown  in  the  fol- 
lowing table,  from  which  it  appears  that  the  total  energy  katabolized,  especially 
when  computed  per  kilogram  of  live  weight,  was  approximately  the  same  on 
the  different  days. 

Constancy  of  katabolism  of  fasting  dog — Voit. 


Total  en- 

Day. 

Live 
weight. 

Energy 
from 
protein. 

Energy 
from 
fat. 

Total 
energy. 

ergy  per 
kilogram 
live 

weight. 

Kilos. 

Calorics,1 

Calories.^ 

Calories.1 

Calories.1 

Second  day  

32.87 

289.3 

816.  9 

1,106.2 

33.66 

Fifth  day                                   

31.67 

142.2 

978.5 

1.120.7 

35.38 

Eighth  day.             

30.54 

117.2 

942.  4 

1,059.6 

34.70 

1  Throughout  this  bulletin  the  word  "  calork 
unless  the  contrary  is  specifically  stated. 


signifies  the  large,  or  kilogram,  calorie, 


The  same  constancy  is  illustrated  by  Rubuer's  experiments  on  a  rabbit,  a 
dog,  and  a  guinea  pig,  whose  relative  protein  katabolism  was  tabulated  on 
page  13.  The  latter  is  repeated  in  the  following  table,  together  with  the 
heat  production  as  measured  directly  or  the  carbon  dioxid  excreted,  which  may 
be  assumed  to  be  an  approximate  measure  of  the  energy  katabolized.  As  the 
table  shows,  notwithstanding  very  considerable  variations  in  the  relative 
amount  of  protein  katabolized,  the  total  energy  liberated  in  the  body  was  rela- 
tively very  constant. 


CONSTANCY   OF   ENERGY    KATABOLISM. 
Constancy  of  kataboHsm  of  fasting  animals — Rubner. 


15 


Day  of  fasting. 

Guinea  pig. 

Dog. 

Rabbit. 

Protein  ka- 
tabolismin 
per  cent  of 
total  ka-    ! 
tabolism. 

Heat  pro- 
duction 
per  kilo- 
gram. 

Protein  ka- 
tabolism  in 
per  cent  of 
total  ka- 
tabolism. 

Carbon 
dioxid  per 
kilogram. 

Protein  ka- 
tabolism  in 
per  cent  of 
total  ka- 
tabolism. 

Carbon 
dioxid  per 
kilogram. 

First 

Calories. 
149.9 
162.6 
156.5 
140.5 
137.3 
150.6 
157.4 
155.  6 
162.6 

Grams. 
20.  70 
17.83 

Grams. 

Second           

10.4 
11.1 
11.0 
11.9  i 
11.8  i 
6.9 

11.2   : 

10.9 

Third    

16.3 

16.5 

Fourth 

17.99 

Fifth                           

23.6 

j           17.26 

Sixth  

Seventh                              .  . 

1           15.90 

Eighth                

Ninth    

126.5 

1            29.8 

50.1 
|            96.4 

115.90 
15.  65 

Tenth  

13.  1 

15.5 
17.4 
20.0 

f          18.70 
\          17.86 
16.13 
17.06 
16.12 

Eleventh               

Twelfth    

17.18 
15.  81 
15.95 
I            15.90 

Thirteenth 

Fourteenth 

Fifteenth  

Sixteenth           

Seventeenth  

Eighteenth 

1 

Benedict *  lias  obtained  like  results  for  the  heat  production  of  man  as  meas- 
ured directly  by  means  of  the  respiration  calorimeter.  For  example,  in  an 
experiment 2  covering  seven  days  the  following  quantities  of  energy  were  ka- 
tabolized  daily. 

Constancy  of  kataboHsm  of  fasting  man — Benedict. 


Protein 

Energv 

katabo- 

Day of  fasting. 

Energy 
from 
protein. 

Energy 
from  fat. 

Energy 
from 
glycogen. 

Total 

energy. 

per  kilo- 
gram 
body 

Hsm  in 
per  cent 
of  total 

weight. 

katabo- 

Hsm. 

Calories. 

Calories. 

Calories. 

Calorie.'. 

Calorics. 

Per  cent. 

First  dav                  -                       ... 

31S 

1,175 

272 

1,765 

29.7 

17.7 

Second  dav         

286 

1.3S5 

97 

1,768 

29.9 

16.0 

'I  hird  dav 

303 

1,471 

23 

1,797 

30.8 

17.0 

Fourth  dav                .          

24S 

1,422 

105 

1.775 

30.8 

14.3 

Fifth  dav 

991 

1  394 

34 

1.049 

29.0 

13.5 

Sixth  dav 

218 

1,244 

01 

1.553 

27.5 

14.  1 

Seventh  dav                 

204 

1.2S6 

7S 

1.568 

2S.O 

]:;.'-> 

This  constancy  of  the  fasting  katabolism  evidently  is  in  accord 
with  the  conception  of  it  outlined  on  page  9  as  the  measure  of  the 
energy  necessary  to  carry  on  the  vital  activities  of  the  body.  The 
functions  of  circulation,  respiration,  excretion,  etc.,  must  go  on  con- 
tinually in  a  state  of  so-called  rest,  the  muscular  tonus  must  be 
maintained  and  divers  minor  muscular  movements  executed.  In 
the  aggregate  all  these  result  in  the  expenditure  of  a  relatively 
uniform  amount  of  energy  from  day  to  day.  This  energy  in  the 


1  The  Influence  of  Inanition  on  Metabolism.     Carnegie  Institution  of  Washington,  1907, 
I'ublication    No.    77. 

"  Experiment  No.  75  on  S.  A.  B.,  pp.  188,  48^,  and  4UO. 


16  MAINTENANCE    RATIONS    OF    FARM    ANIMALS. 

fasting  animal  is  supplied  mainly  by  the  katabolism  of  protein  and 
fat.  In  the  intermediate  stages  of  fasting,  as  has  been  shown,  the 
katabolism  is  largely  that  of  fat,  but  the  ratio  between  fat  and 
protein  katabolized  may  differ  widely  according  to  circumstances. 
In  other  words  the  protein  requirement,  or  at  least  the  amount  of 
protein  used,  may  vary,  while  the  energy  requirement  remains  nearly 
constant.  The  fasting  organism  requires  a  definite  quantity  of 
energy,  but  seems  more  or  less  indifferent  as  to  its  source. 

THE   ENERGY   REQUIREMENT   FOR   MAINTENANCE. 

In  the  fasting  animal  the  store  of  potential  energy  in  the  body 
is  diminished  daily  by  the  amount  required  to  carry  on  the  vital  ac- 
tivities, this  amount  being,  as  just  shown,  relatively  constant.  In 
order  to  prevent  such  a  loss  and  maintain  the  store  of  body  energy, 
it  is  evident  that  a  corresponding  quantity  of  energy  must  be  sup- 
plied in  the  feed  and  that  a  maintenance  ration  is  one  which  supplies 
this  requisite  quantity. 

REPLACEMENT  OF  NUTRIENTS. 

For  this  purpose  experiments  have  shown  that  the  various  di- 
gestible nutrients  may  replace  each  other  or  the  ingredients  of  the 
bodv  through  a  verv  wide  range. 


FKKU  FAT  AND  1?O1)Y  FAT. 


Fat  fed  to  a  previously  fasting  animal  diminishes  or  suspends  the 
loss  of  body  fat.  The  following  averages  of  Pettenkofer  and  Voifs 
experiments,1  computed  from  Atwater  and  Langworthy's  digest,2 
may  serve  to  illustrate  this  substitution  of  feed  fat  for  body  fat : 

Replacement  of  body  fat  by  feed  fat— Pettenkofer  and  Voit. 


None 

UK)  prams  fill 


Food. 

Number 
of  experi- 

Gain  or 
bo 

loss    by 

iy. 

ments. 

Nitrogen. 

Fat. 

drams. 
-6.64 

Grams. 
—  97.76 

) 

—  4.  !K) 

-  10.25 

1 

—  7.70 

1-113.60 

The  smaller  amount  of  fat  not  only  diminished  the  protein  katabolism  but 
;ilso  largely  reduced  the  loss  of  fat  from  the  body.  While  the  larger  amount 
of  fat  showed  a  tendency  to  increase  the  protein  katabolism,  it  not  only  sus- 
pended the  loss  of  body  fat  but  caused  a  storage  of  fat  in  the  organism.  Of 
murse  there  is  no  means  of  distinguishing  in  such  a  case  between  feed  fat  and 


1  Xcilsclirifi    fiir    I'.iiilogii-.    vol.    5,   p.    .",70. 
I  .    S.    lirpart-nent    .,f   Agriculture,   Onke   of  Experiment    Stations,    Hulletin  45. 


REPLACEMENT   OF   NUTRIENTS. 


17 


body  fat,  but  it  is  most  natural  to  suppose  that  the  resorbed  fat  of  the  feed, 
being  already  in  circulation  in  the  body,  is  more  easily  accessible  to  the  active 
cells  than  the  stored-up  fat  of  the  adipose  tissue  and  is  therefore  metabolized 
in  preference  to  the  latter.  • 


CARBOHYDRATES    AND    BODY    FAT. 


Experiments  precisely  similar  to  those  on  fat  just  described  show 
that  carbohydrates  may  also  diminish  or  suspend  the  loss  of  body  fat. 
This  may  be  illustrated  by  the  results  of  three  experiments  upon  a  dog 
by  Rubner. 

Replacement  of  body  fat  by  carbohydrates — Rubner. 


Food. 

Total  nitro- 
gen of  ex- 
creta. 

Total  car- 
bon of  ex- 
creta. 

Gain  or 
loss  of  fat. 

None  

Gram*. 
1.94 

Grams. 
38.18 

Grams. 
-40.99 

1  45 

43  10 

8  41 

104.97  grams  cane  sugar  

1.07 

47.78 

+    .51 

None     

1.42 

26.47 

—28.  10 

42  96  grams  starch          

1.53 

33.28 

—  10.54 

None                      

2.00 

31.53 

—32.  10 

57.38  grams  starch  

1.52 

39.67 

—  10.  74 

CARBOHYDRATES    AND    FEED    FAT. 

Rubner  substituted  dextrose  for  fat  in  the  diet  of  a  dog  receiving 
also  a  fixed  amount  of  lean  meat.  The  results  of  this  substitution 
are  given  in  the  following  table,  and  show  that  with  the  larger 
amount  of  dextrose  in  place  of  the  fat  previously  fed  the  loss  of  body 
fat  was  prevented : 

Replacement  of  feed  fat  by  carbohydrates — Rubner. 


Hation. 

Feed  per  day. 

Gain  or  loss  by 
animal. 

Meat. 

Fat. 

Dextrose. 

Nitrogen. 

Carbon. 

Grams. 
300 
300 
300 
300 
300 

Grams. 
42 
50 

Grams. 

Grams. 
+1.81 
+  .10 
+  1.78 
+2.28 
+  1.98 

Grams. 
+1.27 
+9.31 
-7.44 
-8.15 
+6.21 

Do 

Meat  and  dextrose                                             

63.7 
79.7 
115.5 

Do 

Do 

FEED    PROTEIN    AND    BODY    FAT. 


It  has  already  been  shown  that  body  protein  may  replace  body  fat 
in  the  katabolism  of  the  fasting  animal.  A  similar  substitution  of 
feed  protein  for  body  fat  may  take  place.  When  protein  is  given 
to  a  previously  fasting  animal  it  is  a  well-known  fact  that  the 
nitrogen  of  the  protein  is  rapidly  split  off  and  excreted,  while  the 
nonnitrogenous  portion  of  the  molecule  serves  as  a  source  of  energy 
84S9°— Bull.  143—12 2 


18 


MAINTENANCE  RATIONS   OF   FARM  ANIMALS. 


to  the  organism.  (Compare  pp.  78  to  82.)  This  nonnitrogenous 
residue  can  be  substituted  for  body  fat,  as  is  illustrated  in  an  experi- 
ment by  Rubner  in  which  extracted  lean  meat  was  given  to  a  fasting 
animal,  with  the  result  tabulated  below : 

Replacement  of  body  fat  by  protein — Rubner. 


Nitrogen 
of  food. 

Nitrogen 
katabo- 
lized. 

Fat  katab- 
olized. 

Fasting.. 

Grams. 
0 

Grams. 
5  25 

Grams. 
84  39 

Fed  

35.22 

26.37 

28  37 

Difference  

+21.  12 

50  02 

FAT  OR  CARBOHYDRATES  AND  PROTEIN. 


A  certain  minimum  of  protein  is  essential  to  the  maintenance  of 
the  protein  tissues  of  the  body,  but  feed  protein  in  excess  of  this 
amount  undergoes  rapid  katabolisrn  and  serves  substantially  as  a 
source  of  energy.  Such  an  excess  of  protein  in  the  feed  can  be  re- 
placed by  nonnitrogenous  nutrients,  particularly  the  carbohydrates. 
This  effect  of  fat  or  carbohydrates  as  a  substitute  for  protein  may  be 
illustrated  by  the  following  tabulation  of  the  average  results  of  a 
number  of  Pettenkofer  and  Voit's  experiments : 

Replacement  of  feed  protein  by  fat  or  carbohydrates — Pettenkofer  and  Yoit. 


Feed  per  day. 


Gain  or  loss  by  body. 


Rations. 

Meat. 

Fat. 

Starch-       S*    ,  Nitrogen. 

Carbon. 

Protein  only: 

Grams. 
1.500 

Grams. 

Grams.       Grams.    !    Grams. 
0 

Grams. 
+  3.3 

Average  of  all  (22  experiments)  

1.500 

+0.0 

+  8.7 

Protein  and  fat: 

500 

100 

+     3 

+  27  1 

500 

200 

-  .6 

+  07.3 

Protein  and  carbohydrates: 

500 

5.  3 

200                              -1.8 

+  9.0 

500 

'            2IH)           —1.3 

+   7.2 

It  appears,  then,  that  all  the  principal  nutrients  may  serve  to  supply 
energy  to  the  body,  and  the  facts  just  considered  show  a  remarkable 
degree  of  flexibility  on  the  part  of  the  animal  organism  as  regards 
the  nature  of  the  material  which  can  be  utilized  for  its  metabolism. 
Aside  from  the  small  minimum  of  protein  required,  the  metabolic- 
activities  of  the  body  may  be  supported  now  at  the  expense  of  the 
stored  body  fat,  now  by  the  body  protein,  and  again  by  the  protein, 
the  fats,  or  the  carbohydrates  of  the  feed.  Whatever  may  be  true 
economically,  physiologically  the  welfare  of  the  mature  animal  is  not 
conditioned  upon  any  fixed  relation  between  the  classes  of  nutrients 
in  its  feed  supply  apart  from  the  minimum  requirement  for  protein. 


MAINTENANCE    RATIONS    OF    FARM    ANIMALS.  19 

AVAILABILITY   OF   ENERGY. 

Since  the  chief  function  of  the  feed,  aside  from  a  minimum  of 
protein,  is  to  supply  energy,  it  would  be  natural  to  suppose  that  the 
quantity  of  energy  liberated  in  the  body  by  the  oxidation  of  any 
given  substance  (i.e..  its  metabolizable  energy)  would  be  the  measure 
of  its  nutritive  value.  If  onegramof  starch,  for  example,  can  liberate 
4.2  calories  of  energy  in  the  body  and  a  gram  of  fat  9.5  calories, 
apparently  the  relative  values  of  the  two  should  be  in  proportion  to 
these  figures.  But  while  the  metabolizable  energy  of  the  feed  rep- 
resents the  maximum  amount  of  energy  which  can  be  extracted  from 
it  by  the  organism,  it  does  not  follow  that  all  of  it  can  be  utilized  for 
maintenance.  Energy  is  not  something  which  can  be  fed  into  the 
organism  regardless  of  its  source,  like  fuel  under  a  boiler.  Whatever 
energy  is  in  essence,  so  far  as  the  animal  is  concerned  it  is  carried 
as  chemical  energy  by  the  compounds  of  the  feed,  and  these  must  be 
such  as  can  take  part  in  the  actual  chemical  changes  occurring  in  the 
cells  if  their  energy  is  -to  be  utilized.  The  body  can  not,  like  a  heat 
engine,  avail  itself  of  energy  in  the  kinetic  form.  It  is  quite  con- 
ceivable that  a  compound  might  be  resorbed  from  the  digestive  tract 
and  then  simply  oxidized  to  get  rid  of  it  without  its  entering  into 
the  cell  metabolism.  Its  energy  would  be  metabolized,  that  is,  con- 
verted into  the  kinetic  form,  but  it  would  be  simply  a  source  of  heat 
and  not  of  other  forms  of  energy.  Somewhat  similar  is  the  case  of 
the  chemical  changes  occurring  in  the  digestive  tract.  Some  of  these, 
notably  the  fermentations  of  the  feed,  set  free  energy  as  heat,  yet 
this  energy  plays  no  part  in  the  actual  metabolism  of  the  tissues.  It  is 
clear,  then,  that  we  are  not  warranted  in  concluding  that  because, 
for  example,  a  fasting  animal  breaks  down  body  substance  equivalent 
to  10  therms  per  day,  therefore  a  ration  containing  10  therms  of 
metabolizable  energy  will  suffice  to  maintain  the  animal.  That  will 
depend  upon  how  completely  the  body  is  able  to  use  the  10  therms  of 
metabolizable  energy  supplied  to  it.  In  other  words,  the  energy  must 
not  only  be  present,  but  it  must  be  available  energy. 

If  the  metabolizable  energy  were  all  available  to  protect  body 
tissue  from  oxidation,  then  giving  feed  to  a  fasting  or  partially 
fasting  animal  would  be  practically  the  substitution  of  one  kind  of 
fuel  for  another,  and  the  total  heat  production  would  remain  the 
same.  It  is,  however,  an  observation  as  old  as  the  time  of  Lavoisier 
that  the  consumption  of  feed  tends  to  increase  the  heat  production 
of  an  animal.  That  investigator  observed  the  oxygen  consumption 
of  man  to  increase  materially  (about  37  per  cent)  after  a  meal,  and 
subsequent  experiments  by  a  large  number  of  investigators  have  fully 
confirmed  these  earlier  results,  so  that  the  fact  of  an  increased  metab- 
olism consequent  upon  the  ingestion  of  feed  is  undisputed.  It  is 
especially  to  the  investigations  of  Zuntz  and  his  associates  that  we 


20 


MAINTENANCE   EATIONS   OF   FARM   ANIMALS. 


owe  the  unquestionable  demonstration  of  this  fact  and  of  its  signifi- 
cance in  relation  to  the  nutritive  values  of  feeding  stuffs. 

These  relations  may  perhaps  be  more  clearly  apprehended  through 
an  illustration  taken  from  actual  experimental  work. 

AVAILABILITY    FOB    CATTLE. 

In  an  experiment  by  Armsby  and  Fries1  a  steer  averaging  373.7 
kilograms  live  weight  was  fed  daily  3.2  kilograms  of  timothy  hay. 
an  amount  known  to  be  insufficient  for  maintenance.  The  potential 
energy  contained  in  the  feed,  the  losses  in  the  various  excreta,  and 
the  metabolizable  energy  of  the  ration  were  determined,  with  the 
following  results: 

Per  duy  and  head. 
Feed :  Therms. 

3.199  kilos  timothy  bay _  12.618 

Excreta :  Therms. 

4.786   kilos   feces 5.247 

3.943  kilos  urine .627 

0.079   kilo   methauo_-  _  1.0-17 


Total  _  6.  931 


Metabolizable  energy  of  ration 5.687 

A  balance  experiment  with  the  respiration  calorimeter  showed, 
as  was  expected,  that  the  steer  was  living  in  part  at  the  expense  of 
his  own  tissues,  the  total  loss  of  protein  and  fat  being  equivalent 
to  2.377  therms 2  per  day. 

In  the  period  immediately  following  this  one  the  same  steer  ate 
per  day  5.194  kilograms  of  the  same  timothy  hay.  all  the  other  condi- 
tions of  the  experiment  being  as  nearly  identical  as  possible.  The 
metabolizable  energy  of  this  larger  ration,  determined  in  the  manner 
just  indicated,  was  9.202  therms.3  while  a  balance  experiment  showed 
that  the  loss  of  protein  and  fat  had  been  reduced  to  the  equivalent 
of  0.357  therm.3 

The  following  comparison  of  the  two  periods  can  therefore  be 
made: 

Available  energy  of  ti  mot  hit  //«;/. 


Ration. 

Metaboliz- 
able 
energy  of 
ration. 

Energy  of 
fat    and 
protein  lost 
by  animal. 

Timothy  hay  

Kilos. 
5.294 

Therms. 
9.2»i2 

Therms. 
0.  357 

Do..   .                            

3.199 

5.  687 

2.  :i77 

Differenee...  2.095 


2.020 


'Bureau  of  Animal  Industry.  Hull. 'tin   TJS.  \<\>.   177  :iml  1S4. 

4  Oompiitfd  to  1L'  hours'  standing. 

5  Corrected   to  the  same  live  weight   ns   in    Period    III. 


AVAILABILITY   OF   ENERGY   FOR   CATTLE.  21 

On  the  lighter  ration,  the  steer  supplemented  the  energy  derived 
from  its  feed  by  '2.877  therms  derived  from  the  katabolism  of  its  own 
fat  and  protein,  but  when  2.1  kilograms  of  timothy  hay  was  added  to 
the  ration,  the  amount  of  energy  which  had  to  be  furnished  by  the 
body  tissues  was  reduced  to  0.357  therm.  In  other  words,  2.1  kilo- 
grams of  timothy  hay  supplied  2.020  therms  of  energy  which  was 
available  to  support  the  necessary  bodily  activities  and  which,  there- 
fore, could  replace  an  equal  amount  which  would  otherwise  have  been 
derived  from  the  katabolism  of  body  substance.  This  was  the  con- 
tribution which  this  amount  of  hay  made  to  the  maintenance  of  the 
steer. 

But  the  2.1  kilograms  of  timothy  hay  added  to  the  ration  supplied, 
as  the  table  shows,  3.575  therms  of  metabolizable  energy.  Clearly, 
then,  a  unit  of  metabolizable  energy  supplied  by  the  digestible  matter 
of  the  hay  was  less  efficient  than  the  same  amount  supplied  by  body 
substance.  Only  5G.5  per  cent  of  it  could  be  substituted  for  that  pre- 
viously supplied  by  the  katabolism  of  the  fat  and  protein  of  the  body 
of  the  steer,  while  the  remaining  1.555  therms,  or  43.5  per  cent,  sim- 
ply increased  the  heat  production  of  the  animal,  the  latter  being  as 
follows : 

Daily  lieat  product  fan.1 

Therms. 
On  the  heavier  ration !).  (Jll) 

On   the   lighter   ratinn__  _  S.  004 


Tt  is  customary  in  such  a  case  to  speak  of  the  2.020  therms  as  the 
available  energy  of  the  hay  added  to  the  basal  ration  of  Period  III 
and  to  say  that  56. 5  per  cent  of  the  metabolizable  energy  of  the  hay 
was  available.  Such  a  method  of  statement  does  not  necessarily 
imply  that  the  remaining  43.5  per  cent  served  no  useful  function  in 
the  body,  but  simply  asserts  that  the  net  result  to  the  organism  was 
the  same  as  if  50. 5  per  cent  of  the  metabolizable  energy  were  sub- 
stituted unit  for  unit  for  energy  derived  from  the  katabolism  of  body 
substance  and  as  if  the  remaining  43.5  per  cent  were  useless.  What 
the  experiment  really  shows  is  that  a  unit  of  metabolizable  energy 
in  the  hay  had  only  5G.5  per  cent  of  the  value  for  maintenance  of  a 
unit  of  metabolizable  energy  in  the  body  substance  (chiefly  fat) 
previously  katabolized,  but  the  first  method  of  expression  is  both 
common  and  convenient  and  may  be  retained. 

Experiments  by  the  same  authors  on  several  other  feeding  stuffs  have 
given  results  of  the  same  general  character  as  those  just  quoted.  Of  the 
metabolizable  energy  of  these  feeding  stuffs,  as  directly  determined  in  each  ex- 

1  Corrected  to  1-  hours  standing. 


22  MAINTENANCE  RATIONS   OF   FARM   ANIMALS. 

periinent,  the  following  percentages  were  found  to  be  available  in  the  above 
sense,  while  the  remainder  simply  served  to  increase  the  heat  production : 

Average  a-vailabiUty  of  mctabolizaUe  energy. 

Per  cent. 

Timothy  hay.   5  experiments 50.  32 

Clover  hay,  2  experiments r>8.  47 

Corn   meal,    1    experiment _  09.12 

Wheat  bran.   2   experiments ;"».  30 

Mixed  grain  (1  part  wheat  bran.  3  parts  corn  meal,  3  parts 

linseed   meal   O.   P.),   4   experiments 57.42 

Kellner's1  extensive  investigations  upon  the  metabolism  of  fattening  cattle 
have  likewise  demonstrated  that  in  the  productive  feeding  of  these  animals 
only  part  of  the  metabolizable  energy  supplied  in  excess  of  the  maintenance 
ration  is  recovered  in  the  gain  produced,  the  remainder  being  converted  into 
heat,  so  that  the  heat  production  increases  with  the  amount  of  feed  consumed. 

AVAILABILITY    FOR    THE    HORSE ZUNTZ    AND    HAGEMANN'S    RESULTS. 

The  foregoing  results  upon  cattle  have  been  cited  because  they 
illustrate  simply  and  clearly  the  basic  conception  of  the  availability 
of  feed  energy  and  also  because  they  are,  so  far  as  the  writer  is 
aware,  the  first  experiments  upon  farm  animals  on  submaintenance 
rations  in  which  the  complete  balance  of  matter  and  of  energy  for  24 
hours  has  been  determined.  Zuntz  and  Hagemann  -.  however,  had 
shown  several  years  before  in  an  extensive  investigation  that  the  in- 
creased metabolism  which  Zuntz  and  his  associates  had  observed  in 
dogs  and  men  as  resulting  from  the  ingestion  of  food  was  even  more 
marked  in  the  case  of  the  horse. 

In  their  investigations  the  respiratory  exchange  of  the  animal  was  determined 
by  the  Zuntz  method  in  short  periods  at  various  intervals  after  the  consump- 
tion of  more  or  less  diverse  rations,  a  small  correction  being  added  for  cuta- 
neous and  intestinal  respiration.  By  combining  these  results  with  those  of  a 
number  of  separate  digestion  trials  in  which  the  nitrogen  and  carbon  of  the 
feed  and  of  the  visible  excreta  were  determined,  an  approximate  determination 
of  the  total  energy  metabolism  of  the  animal  was  also  possible.3 

For  example,  on  the  average  of  a  number  of  experiments  in  which  the  metab- 
olism shortly  before  feeding  in  the  morning,  shortly  after  feeding,  and  some 
hours  later  was  determined  by  the  methods  just  outlined,  the  following  results, 
computed  per  kilogram  per  minute  were  obtained.4 

Oxygen          Energy 
consumed,     liberated. 

Gram- 
r.  c.  calories. 

Fast  ing 3. 339  lt>.  929 

'ffi  minutes  after  feeding 3.  &4S  Is.  510 

3J  hours  after  feeding 3.  704  18. 787 


1  Die    Landwirtschaftlichen    Vcrsuchs-Statlonen,    Band    r>n,    and    Erniilming    dor    I.and- 
wirtshaftlichi>n  Xutztiere. 

2  Landwirtscliaftliche  Jahrbilcher,  vol.  27,  Kr^anzungsband  III. 

"  FVir  a   more  complete  a  .-count  of  the  method,   compare   Armshy,   Principles  of  Animal 
Nutrition,    pp.    .'i.SO-Ii.ST. 
*  I.oc.  fit.,  p.  2.82. 


AVAILABILITY   OF   ENERGY   FOR  THE    HORSE. 


23 


It  was  also  found  that  coarse  fodder  (hay)  produced  a  much  more  marked 
effect  than  did  grain.  The  following  comparison  of  the  average  of  the  experi- 
ments of  period  c  on  an  exclusive  hay  diet  with  that  of  the  experiments  of 
period  /  on  a  mixed  ration  illustrates  this  fact.1 


Period  c. 

Period  /. 

Time  since  last  fed  

hours.  . 

2.6 

2.8 

Ration: 
Hay  

...kilos.. 

About  10.  5 

4.75 

Oats.  . 

do 

0.00 

Straw  

do 

1.00 

Total  digested  nutrients  (fat  X  2.4)  
Per  kilogram  and  minute: 
Oxygen  consumed  

grams., 
cubic  centimeters 

4,125 
3.  9837 

5,097 
3.  G98G 

Carbon  dioxid  given  off. 

do 

3  0580 

3  0095 

Energy  set  free  (computed)  .... 

gram-calories 

19.  552 

18  339 

Knergy  katabolism  per  day  and  head  

.calories 

12,450 

11,678 

DIOESTIVK   WORK    FOR   CRUDE   FIBKU. 

Zuntz  and  Ilagemann  estimate  the  fuel  value  of  Ihe  total  digestible  nutrients 
in  the  feed  of  the  horse  (including  digestible  crude  fiber  and  digestible  fat  X 
2.4)  at  3.1)0  calories  per  gram,  and  on  the  basis  of  experiments  on  man  made  by 
Magnus-Levy  in  Zuntz's  laboratory  they  assume  that  9  per  cent  of  the  rnetabo- 
lizable  energy  of  the  digestible  nutrients  as  thus  computed  is  expended  in 
their  digestion.  The  hay  ration  of  the  foregoing  table  contained  1,572  grams 
less  of  (estimated)  digestible  nutrients  than  the  mixed  ration.  The  corre- 
sponding expenditure  of  energy  in  the  digestion  of  these  nutrients  (9  per  cent 
of  their  metabolizable  energy)  equals  580  calories.  Accordingly  the  energy 
katabolism  should  have  been  580  calories  less  in  period  c  than  in  period  /. 
It  was  actually  772  calories  greater,  a  difference  of  1,352  calories.  This  differ- 
ence is  ascribed  to  the  presence  in  the  hay  ration  of  048  grams  more  of  total 
crude  fiber  and  corresponds  to  2.080  calories  per  gram  of  the  latter. 

WORK    OF    MASTICATION. 

The  foregoing  computations  relate  to  the  expenditure  of  energy  in  the  diges- 
tion of  the  food  after  it  has  entered  the  stomach.  The  same  authors  have  also 
determined  the  increase  in  the  gaseous  exchange  caused  by  mastication,  deglu- 
tition, etc.  For  this  purpose  they  compare2  the  excretion  of  carbon  dioxid  and 
the  consumption  of  oxygen  during  the  time  actually  occupied  in  eating  with 
the  corresponding  amounts  during  rest,  as  shown  by  the  average  of  a  number  of 
experiments  made  under  identical  conditions.  On  the  assumption  that  the  pro- 
tein metabolism  is  unaltered,  the  amounts  of  carbohydrates  and  fat  metabo- 
lized and  the  corresponding  amounts  of  energy  are  calculated.  The  following 
is  a  summary  of  the  results  computed  per  kilogram  of  feed  : 

Energy  ('.r/tcmlcd  in  mastication  of  1  kilogram — Zuntz  anil  Hagcmann. 


Feed. 

Number 
of 
experi- 
ments. 

Oxygen 
consumed. 

COj 
excreted. 

Equivalent 
energy. 

Oats  and  cut  straw  (6:1)  

8 

Liters. 
12.964 

Liters. 
10.  679 

Calories. 
64.17 

Hay.                            

8 

33.840 

27.  813 

167.44 

1  Lay,  oats,  and  cut  straw  

8 

20.072 

17.  677 

100.79 

Maize  and  cut  straw  (6:1)  

2 

7.133 

6.205 

35.72 

Green  alfalfa  

7 

6.  171 

4.980 

30.42 

Computed  for  oats  alone             

47.00 

Computed  for  maize  alone  





13.80 

1  I.oi1.   cir.,   pp.   li"(>-270. 


"  Loo.    clt..   p.   271. 


24  MAINTENANCE   RATIONS   OF   FARM   ANIMALS. 

As  was  to  have  been  expected,  the  work  of  mastication  proves  to  be  much 
greater  in  the  case  of  hay  than  in  that  of  grain.  Maize  gave  a  remarkably  low 
result,  while  the  lowest  was  obtained  with  green  fodder.  Even  when  the  results 
on  the  latter  are  computed  per  kilogram  of  dry  matter,  they  are  still  about  40 
per  cent  lower  than  those  on  hay.  A  few  experiments  on  old  horses  with  defec- 
tive teeth  gave  somewhat  higher  results  for  the  mixture  of  oats  and  cut  straw. 

While  pointing  out  that,  as  the  above  results  show,  other  factors  than  the 
amount  of  crude  fiber  influence  the  work  of  mastication,  they  nevertheless 
believe  that  a  sufficiently  close  approximation  for  practical  purposes  may  be 
reached  by  computing  the  work  of  mastication  upon  the  amount  of  crude  fiber 
present,  which  gives  an  average  of  0.565  calorie  per  gram,  and  using  this  factor 
to  compute  the  work  of  mastication  of  the  average  ration.  Adding  this  factor 
to  the  2.086  calories  computed  for  the  work  of  digestion  of  one  gram  of  fiber 
gives  a  total  of  2.65  calories  per  gram  of  total  crude  fiber  as  representing  the 
work  of  mastication  together  with  the  extra  expenditure  of  energy  in  digestion. 

COMPUTATION    OP   AVAILABLE   ENEROY. 

In  brief,  then,  Zuntz  and  Hagemann  compute  the  available  energy, 
or  maintenance  value,  of  a  feeding  stuff  for  the  horse  as  follows: 
First,  the  metabolizable  energy  is  computed  at  the  rate  of  3.9G  calo- 
ries per  gram  of  total  digestible  matter,  including  the  digestible  crude 
fiber  and  the  digestible  fat  multiplied  by  2.4.  Second,  from  the 
metabolizable  energy  thus  computed  there  is  subtracted  9  per  cent 
for  the  work  of  digestion  and  in  addition  2.65  calories  for  each  gram 
of  total  crude  fiber  present. 

The  method  of  computation  may  be  conveniently  illustrated  from 
the  data  given  by  Langworthy1  for  timothy  hay.  Zuntz  and  Hage- 
mann's  factors,  recalculated  per  pound  for  convenience,  become,  for 
metabolizable  energy,  1.796  therms;  for  crude  fiber,  1.202  therms.  On 
this  basis  the  calculation  of  the  available  energy  of  the  hay  would  be 
as  follows: 

Available  energy  in  100  pound*  of  timothy  hay. 

Digestible  nutrients :  Pounds. 

Protein 1.  25 

Crude  fiber 12.39 

Nitrogen-free  extract  21.29 

Fat  (1.1SX2.4)  _.  2.  S3 


37.72 

Total  crude  liber 29.00 

Therms. 

Metabolizable  energy  (1.796  therms X 37. 72) 67.75 

Work  of  digestion  :  Therms. 

1»  per  cent  of  metabolizable  (67.75  therms  X  ().<«)) 6.10 

Additional  for  crude  (1.202  thermsX29)__  _  34.86 


Total   .  40.96 


Available  energy  (maintenance  value) 26.79 

1 1".  S.  Department  of  Agriculture,  Office  of  Experiment  Stations,  Bulletin  12.".  p.  14. 


AVAILABILITY   OF   ENEROY  FOR   THE    HORSE.  25 

As  is  evident  from,  the  brief  description  given  of  the  methods  by 
which  the  factors  are  reached,  this  method  of  computation  is  not 
claimed  by  its  authors  to  be  scientifically  exact,  but  they  believe  it  to 
be  a  sufficiently  close  approximation  on  which  to  base  computations 
of  rations  in  practice. 

Zuntz  and  Hagemann's  conclusions  have  been  subjected  to  con- 
siderable criticism,  the  two  principal  points  being,  first,  their  esti- 
mate of  9  per  cent  for  the  work  of  digestion,  based  upon  the  results 
of  experiments  on  man ;  and,  second,  and  more  especially,  the  assump- 
tion that  the  metabolism  for  24  hours  may  be  computed  from  the 
results  of  comparatively  short  respiration  experiments.  Qualita- 
tively, Zuntz  and  Hagemann  have  clearly  demonstrated  the  very 
considerable  expenditure  of  energy  by  the  horse  in  the  digestion  of 
his  feed,  as  well  as  the  fact  that  this  expenditure  is  much  greater 
Avith  coarse  fodders  than  with  grain,  and  they  were  the  first  to  point 
out  that  this  expenditure  of  energy  must  be  taken  account  of  in  esti- 
mating the  values  of  feeding  stuffs.  There  may  be  a  difference  of 
opinion  as  to  the  quantitative  worth  of  their  figures,  and  certainly 
investigations  by  more  direct  methods,  involving  fewer  assumptions 
and  complex  calculations,  are  greatly  to  be  desired,  but  until  such 
results  are  obtained  we  may  continue  to  use  provisionally  those 
reached  in  the  manner  just  described. 

AVAILABILITY  FOB  THE  HORSE — WOLFF'S  RESULTS. 

His  extensive  investigations  upon  the  working  horse,  made  at 
Hohenheim  in  1877  to  1894 l  and  antedating  the  investigations  thus 
far  mentioned,  led  Wolff  to  a  still  simpler  approximate  method  of 
estimating  what  in  a  sense  corresponds  to  the  available  energy  ot 
the  feed  of  the  horse. 

In  Wolff's  experiments,  the  horse  performed  a  measured  amount  of  work 
which  was  so  adjusted  in  different  periods  as  to  be  as  nearly  as  possible  in 
equilibrium  with  the  feed  consumed.  This  was  considered  to  be  the  case  when 
the  live  weight  of  the  animal  remained  substantially  unchanged  for  a  con- 
siderable period  and  when  the  urinary  nitrogen  did  not  show  an  increase  as  a 
consequence  of  the  additional  work  done.  By  comparing  the  work  performed 
on  a  basal  ration  with  that  which  could  be  done  with  a  heavier  one,  the  ratio 
of  the  work  done  to  the  additional  feed  consumed  was  established  within  the 
limits  of  error  of  the  method,  this  being  the  prime  object  of  the  experiments. 
This  being  determined,  however,  it  was  a  simple  matter  to  compute  the  amount 
of  feed  corresponding  to  the  total  work  done,  while  subtracting  this  from  the 
total  ration  would  give  the  maintenance  ration.  The  results  of  these  compari- 
sons, made  on  the  basis  of  the  so-called  "digestible  nutrients"  of  the  rations 
(the  digestible  fat  being  multiplied  by  24)  are  considered  on  subsequent  pages. 

On  the  average  of  a  considerable  number  of  comparisons,  it  was 
found  that  the  digestible  nutrients  from  coarse  fodders  were  less 

1  Compare  pp.  57  to  ti'2. 


26  MAINTENANCE   RATIONS   OF   FARM   ANIMALS. 

efficient  both  for  work  production  and  for  maintenance  than  were 
those  derived  from  grain,  and  Wolff  also  cites  the  results  of  Gran- 
deau  and  Le  Clerc's  experiments  in  Paris  which  show  the  same 
general  result.  Wolff  shows,  however,  that  if  the  digestible  crude 
fiber  be  omitted  from  the  comparisons,  the  ratio  between  fiber-free 
nutrients  and  the  work  performed  is  comparatively  uniform  and 
also  that  this  assumption  yields  uniform  results  for  the  fiber-free 
nutrients  required  for  maintenance.  He  therefore  concludes  that  the 
crude  fiber  in  the  rations  of  the  horse  is  apparently  valueless  and  that 
the  remaining  digestible  nutrients  may  be  regarded  as  of  equal  value 
whether  derived  from  grain  or  from  coarse  fodders.  Expressed  in 
the  light  of  our  present  conceptions,  this  is  practically  equivalent  to 
saying  that  the  expenditure  of  energy  in  digestion  is  proportional  to 
the  metabolizable  energy  of  the  crude  fiber,  or  that  the  available 
energy  is  proportional  to  the  amount  of  fiber-free  nutrients. 

Wolff  is  careful  to  say  that  the  digestible  crude  fiber  is  apparently 
valueless,  and  virtually  regards  the  amount  of  crude  fiber  as  furnish- 
ing a  convenient  empirical  measure  of  the  difference  in  the  nutritive 
value  of  the  digestible  nutrients  of  coarse  fodder  as  compared  with 
those  of  grain.  That  such  is  the  case  is  doubtless  explained  in  part 
by  the  rather  limited  variety  of  feeding  stuffs  employed  in  the  experi- 
ments. The  coarse  fodder  was  meadow  hay,  with,  in  some  cases,  a 
small  addition  of  straw,  while  the  grain  was  usually  oats,  partially 
replaced  in  some  cases  by  other  feeds.  Whether  the  same  relation 
between  fiber-free  nutrients  and  work  done  would  hold  in  widely 
different  rations  is  not  apparent. 

It  should  be  borne  in  mind  that  in  reality  Wolff's  results  are  rela- 
tive only.  They  do  not  show  the  actual  amount  of  available  energy 
in  the  feed  or  ration,  but  only  that  it  is  proportional  to  the  fiber-free 
nutrients.  The  energy  of  the  latter  would  differ  considerably  from 
the  available  energy  as  computed  by  Zuntz  and  Hagemann's  method, 
first,  because  it  does  not  include  the  deduction  of  0  per  cent  for  di- 
gestive work;  and.  second,  because  it  assumes  a  uniform  value  of  zero 
for  crude  fiber,  while  Zuntz  and  Hagemann's  method  gives  the  crude 
fiber  a  negative  value  if  it  has  a  digestibility  of  less  than  55  per  cent. 
The  values  computed  according  to  Wolff's  method  from  the  fiber-free 
nutrients  are  therefore  considerably  higher  than  Zuntz  and  Hage- 
mann's figures. 


AVAILABILITY    FOR    CARNIVORA. 


For  many  j-ears  it  was  taught,  in  accordance  with  Rubner's  theory 
of  "  isodynamic  replacement  "  (compare  p.  72).  that  with  carnivora 
the  nutrients  were  of  value  in  proportion  to  their  content  of  metab- 
olizable energy.  Uubner's  own  later  investigations,1  however,  have 

1  Die  (Jesetzo  dcs  EncTKievorbrauchs  l>ei  dor  Erniihrung. 


AVAILABILITY    OP   ENERGY   FOB   CARNTVOEA. 


27 


shown  that  what  is  true  of  the  feeding  stuffs  consumed  by  horses  and 
cattle  is  also  true  of  nearly  pure  nutrients  fed  to  dogs.  With  these 
subjects  it  is  possible  to  use  the  fasting  state  as  the  basis  of  compari- 
son, which  considerably  simplifies  the  investigations.  The  experi- 
ments were  made  at  a  comparatively  high  temperature,  namely,  about 
33°  C.,  a  fact  which  is  of  importance,  as  will  appear  later,  in  the  inter- 
pretation of  the  results. 

An  experiment  in  which  nearly  enough  fat  was  fed  to  supply  the 
requirements  of  the  organism  for  energy  gave  the  following  results 
per  kilogram  live  weight,  stated  in  a  form  which  is  somewhat  differ- 
ent from  that  used  by  Kubner  but  which  in  substance  is  identical 
with  it : 

Availability  of  cncryi/  of  fal — Rubncr. 


Metaboliz- 
able 
energy  of 
feed  per 
kilogram 
live  weight. 

Loss  by 
body  per 
kilogram 
live 
weight. 

Fat  fed  

Calorics. 
53  4 

Falories. 
1  5 

Fasting  

0 

54  0 

Difference  

53  4 

46  5 

Percentage  available.  .  . 

87.08 

This  result  appears  somewhat  remarkable  in  view  of  the  fact  that 
the  comparison  is  virtually  with  body  fat.  Literally  interpreted,  it 
means  that  the  energy  of  feed  fat  is  only  87  per  cent  as  valuable  as 
the  energy  of  body  fat  plus  a  little  protein.  If  this  be  true,  it  implies 
a  larger  expenditure  of  energy  in  the  digestion  of  fat  than  now  seems 
probable,  since  the  katabolism  of  resorbed  feed  fat  can  hardly  differ 
greatly  from  that  of  body  fat.  Rubner's  figure  is  the  result  of  a 
single  experiment  and  unfortunately  it  enters  into  the  computation  of 
all  the  other  results.  A  redetermination  of  this  factor  is  much  to  be 
desired. 

In  two  other  experiments,  lean  meat  nearly  equivalent  to  the  main- 
tenance requirement  was  fed.  The  meat  contained  a  small  amount  of 
fat,  the  average  metabolizable  energy  of  the  feed  per  kilogram  live 
weight  being  distributed  as  follows : 

Calories. 

In   protein 56.70 

In  fat 4.05 

61.  65 


28 


MAINTENANCE   RATIONS    OF   FARM   ANIMALS. 


Using  the  data  afforded  by  the  experiment  on  fat,  the  availability 
of  the  energy  of  the  protein  may  be  computed  as  follows : 

Availability  of  energy  of  protein — Rubner. 


Metabolizable 
energy  of  feed 
per  kilogram 
live  weight. 

Loss  by 
body  per 
kilogram 
live  weight. 

Meat  fed 

Calories. 
61  6,5 

Calories. 
S  90 

Fasting                  

0 

51.50 

Difference 

61  65 

42  60 

Difference  due  to  fat.            

4  95 

4.31 

Difference  due  to  protein  

56.70 

38.29 

Percentage  available  

Per  cent. 
67.53 

The  difference  between  the  percentage  available  and  100  shows,  of 
course,  the  proportion  of  the  metabolizable  energy  of  the  feed  which 
was  expended  in  increasing  the  total  metabolism  as  measured  by  the 
heat  production.  This  increase  of  the  metabolism  of  the  body  is 
called  by  Rubner  the  "  specific  dynamic  effect "  of  the  several  nutri- 
ents. Rubner's  final  average  results  are  contained  in  the  following 
table.  It  should  be  clearly  understood  that  they  are  not  applicable 
to  the  "digestible  nutrients"  of  the  feed  of  herbivora. 

A  rerage  availability — liubncr. 


Availa- 
bility. 

Specific 
dynamic 
effect. 

Body  protein  

PIT  cent. 
68.1 
69.1 
72.0 
87.3 
94.2 

Pi  r  cent. 
:u.9 

30.9 
28.0 
12.  7 

5.8 

Meat  protein 

Gelatin                                                        .                 

Fat                         

CAUSES  OF   INCREASED  METABOLISM. 

The  foregoing  paragraphs  have  dealt  with  the  fact  of  the  in- 
creased metabolism  and  consequent  heat  production  resulting  from 
the  ingestion  of  feed  without  considering  the  cause  of  the  increase. 
Two  explanations  of  it  naturally  suggest  themselves.  The  first  is 
that  the  greater  supply  of  the  various  nutrients  directly  stimulates 
the  metabolism  of  the  body  cells,  wrhile  the  second  ascribes  the  in- 
creased metabolism  to  the  additional  expenditure  of  energy  required 
for  the  digestion  of  the  feed  and  its  preparation  for  metabolism  in 
the  actual  vital  processes.  The  latter  explanation  is  the  one  which 
has  been  generalhr  accepted,  although  by  no  means  without  dissent,1 


1  Compare  llcilncr.  X.'itschrift  fiir 


vol.   4S,  p.    144:  vol.  HO,  p.  48S. 


CAUSES    OF    INCREASED    METABOLISM.  29 

and  the  expenditure  of  energy  for  these  purposes  has  been  somewhat 
loosely  and  perhaps  not  altogether  fortunately  designated  as  the 
"  work  of  digestion."  A  consideration  of  some  of  the  processes  con- 
nected with  the  consumption  of  feed  which  lead  to  the  liberation 
of  energy  may  serve  to  clarify  the  conception. 

MECHANICAL    WORK. 

Digestion  requires  more  or  less  mechanical  work  in  the  prehension  and 
mastication  of  the  feed  and  in  moving  it  through  the  digestive  organs.  In  this 
connection,  too,  it  should  be  remembered  that  the  feed  in  this  sense  includes 
the  water  as  well,  three  or  four  parts  of  water  being  usually  consumed  by 
herbivora  for  each  part  of  dry  matter  in  the  feed.  As  noted  on  p.  — ,  Zuntz 
and  Ilageinann  have  compared  the  metabolism  of  the  horse  while  eating  with 
that  of  the  same  animal  while  at  rest  and  computed  from  the  difference  the 
amount  of  energy  expended  in  mastication.  The  following  recapitulation  of 
some  of  their  results  shows  the  number  of  calories  of  energy  expended  in  the 
mastication  of  1  kilogram  of  the  material  named: 

Calorics. 

Hay _  1(57.  r> 

Green  alfalfa__  .'50.4 

Oats__  47.0 

Maize 13.  S 

Kellner  1  has  investigated  the  effect  of  the  grinding  of  straw  upon  its  value 
in  a  productive  ration.  He  finds  that  the  practical  elimination  in  this  w;iy  of 
the  work  of  mastication  reduces  the  expenditure  of  energy  by  approximately 
O.G6  calorie  for  each  gram  of  crude  fiber  present  in  the  straw. 

That  the  movement  of  the  masticated  feed  through  the  digestive  tract  must 
also  require  an  expenditure  of  energy  is  obvious,  but  no  data  are  available 
as  to  its  amount. 

SECRETION. 

The  secretion  of  the  digestive  fluids  likewise  requires  some  expenditure  of 
energy.  This  has  been  shown  by  direct  experiment  to  be  true  of  the  salivary 
glands  and  the  pancreas  and  is  also  true,  doubtless,  of  the  other  digestive 
glands.  Apparently,  however,  the  amounts  of  energy  thus  exi>ended  are  com- 
paratively small. 

FERMENTATION. 

The  extensive  fermentations  occurring  in  the  digestive  tract  of  herbivora 
result  in  a  considerable  evolution  of  heat.  The  most  important  of  these  is  the 
methane  fermentation.  Assuming  on  the  basis  of  Tappeiner's  results2  that  100 
grams  of  carbohydrates  yield  4.7  grams  of  methane  and  33.5  grams  of  carbon 
dioxid.  and  assuming  further  that  two-thirds  of  the  carbon  of  the  organic 
acids  produced  is  contained  in  acetic  acid  and  the  remainder  in  butyric,  it  may 
be  computed  that  the  heat  evolved  amounts  to  12.5  per  cent  of  the  total  energy 
of  the  digested  carbohydrates  or  0-523  calorie  per  gram.  It  should  be  noted 
that  this  estimate  does  not  refer  to  the  potential  energy  carried  off  in  the 
methane,  but  to  the  heat  evolved  in  the  fermentation.  The  latter  is  part  of 
the  metabolizable  energy  of  the  carbohydrates,  since  it  is  liberated  in  the 


1  l)ii<  Krniihruni:  <lrr  Lnndwirtsohaftllchc  Xutztinv,  r>th  »•<].,  p.   It;:1,. 
-Zeitsclirift  fiir  I'.iolojric,  \ol.  UO,  p.  r>L'. 


30  MAINTENANCE   RATIONS   OF   FARM   ANIMALS. 

kinetic  form  in  the  body,  but  since  it  takes  at  once  the  form  of  heat,  it  is  not 
available  energy  in  the  sense  in  which  the  term  is  here  used. 

The  same  general  considerations,  of  course,  apply  to  the  other  fermentations 
and  putrefactions  which  occur  in  the  digestive  tract,  but  their  amount  iu 
herbivora  is  probably  small  compared  with  that  of  the  methane  fermentation, 
and  we  have  relatively  little  knowledge  regarding  them. 

DIGESTIVE   CLEAVAGES. 

It  is  well  known  that  extensive  cleavages  of  the  feed  ingredients  occur  in  the 
digestive  tract.  The  nutrients,  by  the  action  of  the  digestive  ferments,  are  split 
up  into  simpler  atomic  groupings — the  so-called  building  stones  of  the  mole- 
cule— out  of  which  the  proteins,  carbohydrates,  and  fats  peculiar  to  the  animal 
body  are  built  up.  One  argument  which  has  been  brought  forward  in  the  past 
against  the  extensive  occurrence  of  such  cleavages  in  natural  digestion,  espe- 
cially of  the  proteins,  has  been  the  teleological  one  that  the  splitting  up  into 
these  comparatively  simple  compounds  was  a  waste  of  valuable  nutritive  mate- 
rial. On  the  other  hand  these  processes  have  been  invoked  to  explain  the 
striking  effect  of  the  proteins  in  stimulating  the  metabolism — their  large  specific 
dynamic  effect,  to  use  Rnbner's  terminology.  So  far  as  the  peculiar  use  of  pro- 
tein in  the  body  is  concerned,  it  is  well  established  that  its  crystalline  cleavage 
products  can  be  resynthesized  to  form  protein.  It  is  of  special  interest,  there- 
fore, to  learn  that  these  cleavages  and  resyntheses  are  apparently  nearly  isother- 
mic  processes.  Some  of  the  cleavage  products  of  protein  contain  more  potential 
energy  per  gram  than  protein  itself,  as,  for  example,  leucin,  with  6.525  calories 
per  gram,  and  tyrosin,  with  5.916  calories  per  gram.  Others,  like  alanin,  with 
a  heat  of  combustion  of  4.356  calories,  contain  but  little  less  energy  than  the 
protein  from  which  they  are  derived.  Even  the  simplest  amiuo-acid,  glycocol, 
resulting  from  this  cleavage  has  a  heat  of  combustion  of  3.129  calories  per 
gram.  The  impression  which  these  figures  give — that  but  little  energy  is  lost 
in  the  cleavage  of  the  proteins — is  confirmed  by  direct  experiments.  Loewi  * 
found  the  dry  residue  of  the  tryptic  digestion  of  meat  to  have  an  energy  value  of 
4.6  calories  per  gram.  Tangl,  Lengyel,  and  Hari 2  found  the  products  of  the 
peptic  or  tryptic  digestion  of  egg  albumin  and  serum  albumin  to  contain  nearly 
or  quite  as  much  potential  energy  as  the  original  protein.  Grafe 3  has  made  arti- 
ficial digestions  of  protein  in  a  calorimeter,  and  found  no  noticeable  evolution 
or  absorption  of  heat.  It  seems  safe,  therefore,  to  regard  the  digestive  cleavage 
of  protein  as  at  least  a  nearly  isotherruic  process,  causing  little  loss  of  energy  iu 
digestion. 

Substantially  the  same  thing  is  true  of  the  digestive  cleavage  of  carbohy- 
drates and  fats.  Thus  1  gram  of  starch  yields  1.111  grams  of  dextrose,  and 
the  heats  of  combustion  of  these  quantities  are,  respectively,  4.183  calories  and 
4.159  calories,  showing  a  loss  of  less  than  0.6  per  cent.  One  gram  of  sucrose 
yields  0.5264  gram  each  of  dextrose  and  levulose,  and  the  energy  values  are, 
respectively.  3.955  calories  and  3.947  calories,  or  a  loss  of  less  than  0.2  per  cent 
So,  too,  1  gram  of  tristearin  with  a  heat  of  combustion  of  9.43  calories  yields 
by  hydrolysis  0.9573  gram  of  stearic  acid,  equivalent  to  9.026  calories,  and 
0.1033  gram  of  glycerin,  equivalent  to  0.424  calorie,  or  a  total  of  9.45  calories. 

1  Leathes.     Problems  in  Animal   Metabolism,   p.   129. 

2Archiv  fiir  die  gesammte  Physiologic  des  Menschen  und  der  Thiere  (Pfliiger),  vol. 
115,  p.  1. 

3  .Tahrosbericht  fiber  die  Fortschritte  der  Tier  f'hemie,  vol.  37,  p.  917. 


CAUSES   OF    INCREASED   METABOLISM.  31 

INTERMEDIARY    METABOLISM. 

The  chemical  reactions  taking  place  during  the  so-called  intermediary  metabo- 
lism of  the  rcsorbed  material  before  it  is  finally  utilized  for  the  vital  processes 
have  also  to  be  considered  as  possible  sources  of  heat  production,  although  our 
present  knowledge  of  them  is  meager. 

This  possibility  is  of  special  interest  in  connection  with  the  marked  effect  of 
protein  on  the  energy  metabolism,  since  this  can  hardly  be  ascribed  to  digestive 
work  in  the  strict  sense.  In  the  normal  digestion  of  protein  fermentations  play 
a  very  small  part,  while,  as  just  shown,  the  digestive  cleavage  of  protein  is 
substantially  isothermic.  Neither  can  we  imagine  that  the  mechanical  work 
of  digestion  or  the  secretion  of  digestive  juices  can  account  for  the  large 
expenditure  of  energy.  Kubner1  has  reported  experiments  in  which  the  protein 
katabolism  of  the  fasting  animal  was  artificially  increased  by  the  administra- 
tion of  phlorhizin,  and  in  which  a  similar  increase  in  the  heat  production  i.s 
computed,  although  there  could  have  been  no  digestive  work  in  the  strict  sense. 
Falta,  Grote,  and  Stahlein2  have  found  that  the  products  of  the  tryptic  diges- 
tion of  casein  when  fed  to  a  dog  produce  nearly  as  great  an  increase  in  the 
metabolism  as  does  a  corresponding  amount  of  casein,  while  in  the  familiar 
experiments  of  Zuntz  and  Mering3  the  intravenous  injection  of  the  crude  prod- 
ucts of  the  peptic  digestion  of  blood  fibrin  had  a  like  effect. 

The  katabolism  of  protein  seems  to  consist  in  outline,  first,  of  a  hydroly tic- 
cleavage  into  peptids  and  amino-acids  and,  second,  in  a  deamidization  of  these 
latter  compounds,  and  it  is  the  nonnitrogenous  products  resulting  from  this 
deamidization  which  serve  as  a  source  of  energy  for  the  body,  the  nitrogen 
being  split  off  as  ammonia  and  excreted  as  urea.  It  is  to  a  liberation  of 
energy  in  the  form  of  heat  in  these  preliminary  processes  of  preparing  protein 
to  serve  as  fuel  that  Rubner  and  other  authors  ascribe  its  si>ecific  dynamic 
effect. 

Our  knowledge  of  the  intermediary  metabolism  of  protein  is  too  meager  to 
render  any  quantitative  estimate  of  the  amount  of  energy  lost  in  this  way  of 
much  value.  The  cleavage  of  protein,  as  noted,  seems  to  be  substantially  iso- 
thermic. The  deamidization  of  the  simpler  amino-acids  with  a  small  number 
of  carbon  atoms  seems  at  first  thought  to  involve  considerable  loss  of  energy. 
For  example,  the  potential  energy  of  1  gram  of  glycocol  and  of  alauin  and  of 
equivalent  amounts  of  acetic  and  propionic  acids  are: 


filvcocol 


Calorics. 

Knergy  of  amino  acid I        3. 129 

Energy  of  equivalent  fatty  at1  id j        2. 791 


Difference !          .338 

Percentage  loss 10. 8 


Alanin. 


Calorirs. 
4. 350 
4.129 


A  similar  comparison  of  alanin  with  the  equivalent  amount  of  lactic  acid 
shows  an  apparent  loss  of  about  14  per  cent.  With  the  higher  members  of  the 
series,  the  loss  computed  in  this  way  is  relatively  small.  It  must  be  remem- 
bered, however,  that  the  amino  group  is  split  off  as  ammonia,  which  also  con- 

1  Gesot/.o  dos  Energiovorbrauchs  hoi  dor  Krniihrnng. 
-  Beit  nitre  zur  Chomischen  Physiologic  nnd  Pathologic,  vol.  !),  p.  .'!74J. 
"Archiv  fiir  die  gesainmte  Physiologie  des  Mensehcn  und  der  Thicro   (Ptliigon.   vol.  :?:.'. 
p.  199. 


32  MAINTENANCE   RATIONS   OF   FARM   ANIMALS. 

tains  potential  energy  equal,  according  to  Ostwald,  to  3.319  calories  per  gram 
in  the  gaseous  state.  If  we  assume  that  the  alanin  yields  lactic  acid  with  a 
heat  of  combustion  of  3.7  calories  per  gram  we  may  make  the  following  com- 
parison : 

Calories.  Calories. 

Energy  of  1  gram  alauin 4.356 

Energy  of  1.011.  grams  lactic  acid 3.742 

Energy  of  0. 1!)1  gram  ammonia 0.  634 

4. 37G 


Difference .020 

In  other  words,  it  would  appear  that  the  deamidization  of  the  amino  acids, 
like  the  antecedent  cleavage  of  the  proteins,  is  a  nearly  isothermic  reaction  and 
that  we  must  seek  elsewhere  for  the  explanation  of  the  specific  dynamic  effect 
of  protein.  We  can  by  no  means  assert,  however,  that  the  protein  kataholism 
actually  takes  place  according  to  this  simple  scheme,  nor  that  the  nonnitrog- 
enous  substances  resulting  from  deamidization  of  the  amino  acids  yield  their 
energy  without  loss.  It  seems  not  unlikely  that  the  higher  fatty  acids  and  other 
nonnitrogenous  derivatives  of  protein  are  broken  down  by  cleavage  and  other- 
wise to  comparatively  simple  molecules  before  they  are  finally  oxidized,  and 
there  is  the  possibility  of  more  or  less  loss  of  energy  in  such  processes. 

As  already  indicated.  Kubner  explains  the  specific  dynamic  effect  of  protein 
from  the  foregoing  point  of  view,  but  in  a  different  manner.  It  has  been  shown 
beyond  reasonable  doubt  that  sugar  is  produced,  or  may  be  produced,  in  the 
katabolism  of  protein.  According  to  Kubner,  it  is  only  the  energy  of  this  sugar 
that  is  callable  of  being  used  for  the  physiological  functions  of  the  body  cells, 
while  the  energy  set  free  in  the  conversion  of  protein  into  sugar  is  liberated  as 
heat  and  constitutes  the  specific  dynamic  effect.  This  explanation  of  Ilnbner's, 
however,  seems  to  be  disproved  by  recent  results  reported  by  Lnsk  and  Ringer.1 
They  have  shown  that  alanin  is  completely  convertible  to  dextrose  in  a  diabetic 
animal,  while  in  the  case  of  glutauiic  acid  but  three  out  of  the  five  carbon  atoms 
of  the  molecule  are  xitilized  for  the  production  of  dextrose.  According  to  liub- 
ner's  hypothesis,  therefore,  alanin  should  show  no  specific  dynamic  effect,  while 
glutamic  acid  should  show  a  considerable  one.  In  a  preliminary  communication 
Lnsk  2  reports  that  neither  one  of  these  amino  acids  when  added  to  a  standard 
diet  increased  the  excretion  of  carbon  dioxid  in  the  respiration.  This  result  is 
in  striking  contrast  with  those  of  Falta,  Grote,  and  Stithlein  and  of  Zuntz  and 
Mering  just  referred  to,  in  which  the  crude  products  of  tryptic  or  peptic  diges- 
tion were  fed.  They  suggest  that  some  substance  other  than  the  recognized 
amino-acids  may  be  responsible  for  the  stimulating  effect  of  protein  upon  metabo- 
lism, while  they  likewise  recall  the  fact  that  crude  peptones  have  been  found  to, 
have  a  poisonous  effect  when  injected  intravenously  while  purified  peptones  do 
not,  and  likewise  the  fact  that  in  /untz  and  Mering's  experiments  purified 
peptones  caused  no  increase  in  the  metabolism. 

EXCRETION. 

Zuntz "  calls  attention  to  ISarcroft's  '  experiments,  which  show  that  the  excre- 
tory activity  of  the  kidneys  is  accompanied  by  a  notable  increase  in  the 
amount  of  oxygen  consumed,  and  sees  in  the  work  thrown  on  these  organs 
by  the  elimination  of  the  nitrogen  of  protein  one  of  the  causes  of  its  specific 

1  .loiirnnl   of  tin-   Amrrii-:m   Chemical    Society,   vol.   .'il'.  p.  071. 

-  Proceedings  of  Society  for  Kxperimental  I'.iolo^'y  and  Medicine.   MHO,  vol.  7.  p.   1  .".f,. 

'•'  Medi/insclic    Klinik.    1JMO. 

4  Kruebnisse  tier  Physiolouie,  vol.  7,  p.  744. 


THE    MAINTENANCE   RATION.  33 

dynamic  effect.  In  experiments  in  collaboration  with  Steck  he  found  that 
a  marked  increase  of  the  metabolism,  as  computed  from  the  oxygen  consumed, 
followed  the  administration  of  urea,  and  likewise  of  sodium  chlorid,  to 
men  and  dogs.  In  the  case  of  urea  he  computes  (hat  the  effect  was  equal  to 
20  to  25  per  cent  of  that  of  an  equivalent  amount  of  protein.  Zuntz  also  calls 
attention  to  earlier  experiments  by  Xering  and  Schmoll  in  which  carbo- 
hydrates added  to  the  diet  of  a  diabetic  produced  a  similar  increase  of  metab- 
olism, although  the  sugar  was  not  assimilated  but  excreted  unchanged.  Zuntz 
ascribes  the  results  obtained  by  IJubner  to  the  fact  that  phlorhizin  added  largely 
to  the  increased  excretory  work  required  by  the  elimination  of  the  nitrogen  and 
of  the  sugar  formed,  pointing  out  also  that  Ilubner  has  overestimated  the 
amount  of  heat  produced  through  failure  to  deduct  the  energy  of  the  sugar  ex- 
creted in  the  urine.  On  the  other  hand,  in  Lusk's  experiments,  just  quoted, 
there  was  an  increased  excretion  of  urea  subsequent  to  the  administration  of 
amino  acids,  but  no  increase  in  the  carbon  dioxide  excreted,  while  Tangl  *  finds 
that  the  intravenous  injection  of  urea  or  sodium  chlorid  causes  an  increase  in 
the  metabolism  even  when  the  kidneys  have  been  extirpated  or  clamped  off. 

On  the  whole,  it  can  not  be  said  that  any  fully  satisfactory  explana- 
tion has  yet  been  offered  of  the  effects  of  feed,  and  in  particular  of 
protein,  upon  the  metabolism,  although  certain  factors,  especially  in 
domestic  animals,  are  clearly  evident. 

But  whatever  explanation  we  may  accept — whether,  following 
Zuntz,  we  speak  of  work  of  digestion,  or.  with  Rubner.  avoid  any 
implication  as  to  the  cause  by  the  use  of  the  term  specific  dynamic 
effect — the  fact  that  the  metabolizable  energy  of  different  feeding 
substances  is  not  equally  available  for  maintenance  is  established 
beyond  question,  and  it  is  this  fact  whk-h  is  of  immediate  importance 
in  considering  the  energy  requirement  for  maintenance  and  the  main- 
tenance values  of  feeding  stuffs. 

TIIF.    rilAINTKNANfK    RATION. 

In  accordance  with  the  principles  laid  down  in  the  foregoing  para- 
graphs, a  maintenance  ration  as  regard*  energy  may  be  defined  as 
one  which  supplies  available  energy  equal  to  the  fasting  katabolism. 

For  example,  in  Rubner's  experiment  cited  on  page  ^7.  in  which 
fat  was  fed,  the  fasting  katabolism  of  the  dog  was  54  calories  per 
kilogram.  Fat  containing  53.4  calories  of  metabolizable  energy  di- 
minished the  loss  of  body  tissue  by  4(>.5  calories.  Evidently,  then, 
to  reduce  the  loss  by  54  calories,  that  is.  to  reduce  it  to  zero,  would 
have  required  SS^X/ete— ^2  calories  of  metabolizable  energy  to 
be  supplied  in  fat.  The  same  thing  may  also  be  expressed  in  a 
slightly  different  way:  If.  as  there  computed,  only  87.08  per  cent  of 
the  metabolizable  energy  of  fat  is  available,  then  to  make  good  a  total 
loss  of  54  calories  will  require  54-=-0.8708— 02  calories  of  metaboliza- 

1  Biochemische  Zeitschrift.   vol.   "4,  p.   1. 
8489°— Bull.  143—12 3 


34  MAINTENANCE   RATIONS    OF    FARM    ANIMALS. 

ble  energy  in  fat.1  On  this  basis  we  may  compute  from  Rubner's 
final  averages  (p.  28)  that  to  maintain  the  dog  experimented  on, 
that  is,  to  make  good  the  loss  of  54  calories  of  energy  per  kilogram, 
it  would  have  been  necessary  to  supply  per  kilogram  the  following 
amounts  of  metabolizable  energy  in  the  materials  named : 

Calories. 

In  meat  protein 79.3 

la  gelatin  _.  IS.  1 

In   fat 61.9 

In  cane  sugar 57.3 

These  figures  afford  a  simple  illustration  of  the  fact  that  the  amount 
of  metabolizable  energy  required  for  maintenance  is  variable,  being 
greater  as  its  availability  is  less.  The  maintenance  requirement  of 
the  dog  was  54  calories  of  available  energy.  The  maintenance  ration 
needed  to  supply  this  varied  according  to  the  material  which  served 
as  the  carrier  of  the  energy. 

The  same  relations  hold  good  for  farm  animals,  although  the  fact 
that  we  can  not  well  observe  their  fasting  katabolism  directly  makes 
the  computation  a  trifle  more  complicated.  As  an  example,  we  may 
take  the  experiment  on  timothy  hay  already  cited  on  page  20.  The 
addition  of  2.1  kilograms  of  timothy  hay,  equivalent  to  3.575  therms 
of  metabolizable  energy,  to  the  basal  ration  reduced  the  loss  of  energy 
from  the  body  of  the  animal  by  2.020  therms.  Evidently,  then,  to 
have  reduced  it  by  2.377  therms,  that  is.  to  zero,  would  have  required 

the  addition  of  2.1  X  9  O9O  =  2.471  kilograms  of  the  hay,  equivalent 

to  4.207  therms  of  metabolizable  energy.  The  total  maintenance  ration 
of  this  particular  feeding  stuff,  then,  would  have  been  the  basal 
ration  plus  this  amount,  or  5.070  kilograms  of  the  hay,  equivalent  to 
9.894  therms  of  metabolizable  energy. 

The  same  result  may  also  be  obtained  by  the  use  of  the  percentage 
availability  as  computed,  viz.  50.5  per  cent.  The  heavier  ration 
failed  to  maintain  the  animal  by  0.357  therms,  that  is,  it  lacked  this 
amount  of  available  energy.  To  supply  this  requirement  would  evi- 
dently demand  0.357—0.505=0.032  therms  of  metabolizable  energy, 
which  added  to  the  9.202  therms  already  contained  in  the  ration 
gives  a  total  as  above  of  9.894  therms.  The  same  computation  can, 
of  course,  be  made  from  the  lighter  ration  with  the  same  result. 

From  the  data  given  it  is  likewise  possible  to  compute  what  the  loss 
by  the  body  would  have  been  had  it  been  practicable  to  withdraw  all 
feed.  The  basal  ration  contained  5.087  therms  of  metabolizable 
energy,  of  which  50.5  per  cent  was  available;  that  is,  the  basal  ration 
was  capable  of  preventing  the  loss  of  5.087X0.505=3.213  therms  from 

1  On  the  assumption,  of  course,  that  the  effect  is  a  linear  function  of  the  amount  of 
food. 


THE    MAINTENANCE    RATION. 


35 


the  body.  Had  the  basal  ration  been  entirely  withdrawn,  then  tin- 
loss  would  have  been  increased  by  this  amount;  that  is,  the  total  loss 
would  have  been  3.213-j-2.377=5.590  therms.  The  same  quantity 
would,  of  course,  be  obtained  by  starting  from  the  heavier  ration 
or  from  the  maintenance  ration  as  computed  above.  The  fasting 
katabolism,  which  can  not  well  be  determined  directly,  is  thus  ob- 
tained by  computation.  In  other  words,  this  steer  expended  daily 
5.590  therms  of  energy  in  the  maintenance  of  his  necessary  vital  proc- 
esses aside  from  those  connected  with  the  digestion  and  assimilation 
of  his  feed.  This  was  his  maintenance  requirement  as  defined  in  the 
foregoing  paragraphs,  and  an  amount  of  the  clover  hay  which  was 
capable  of  supplying  this  quantity  of  available  energy,  viz,  5.670 
kilograms,  was  a  maintenance  ration,  while  on  smaller  amounts  he 
drew  upon  his  body  tissues  to  cover  the  deficiency. 


Fi<;.   1. —  Availability  of  metabolizable  energy  of  hay. 

All  these  facts  may  also  IK-  conveniently  represented  graphically 
as  follows : 

If  on  the  two  coordinate  axes  of  figure  1,  we  let  the  horizontal  distances 
represent  the  metabolizable  energy  of  the  feed  and  the  vertical  distances  the 
gain  of  energy  by  the  body  of  the  animal,  the  results  of  the  two  experiments  jnst 
referred  to  may  be  represented  by  the  points  \  and  B.  the  distances  OE  (equal 
to  H.OST  therms)  and  OF  (equal  to  !).2U2  therms)  representing  the  amounts  of 
metabolizable  energy  in  the  two  rations  and  the  distances  EA  (.equal  to 
—  2.377  therms)  and  FR  (equal  to  —0.357  therm)  the  corresponding  (negative'' 
gains  of  energy  by  the  animal.  A  straight  line  drawn  through  A  and  H  and  in- 
tersecting the  two  axes  at  1>  and  C  will  then  represent  the  relation  between  the 
supply  of  metabolizable  energy  in  the  feed  and  the  grain  by  the  body  of  the 
animal.1  This  relation  may  also  be  expressed  analytically  by  the  equation 
y~-o.i — in.  in  which  /»  =  ()]>  (equal  to  r>.r>00  therms')  will  represent  the  com- 


1  Asviiiniug  that  this  is  a  linear  function. 


36  MAINTENANCE   RATIONS    OF    FARM    ANIMALS. 

puted  fasting  katabolism  and  a  the  tangent  of  the  angle  between  AB  and  the 
horizontal  axis  (equaling  in  this  case  0.565).  or  the  percentage  availability, 
while  OC  (equal  to  9.804  therms)  is  the  maintenance  ration  in  terms  of  the 
metabolizable  energy  of  this  particular  hay. 

The  fasting  katabolism  being  a  constant  quantity  under  like  con- 
ditions, it  follows  that  an  amount  of  any  feed  capable  of  supplying 
5.590  therms  of  available  energy  would  have  been  a  maintenance 
ration  for  this  animal.  It  is  clear  then  that  the  actual  weight  of 
feed  required  for  maintenance  will  vary  inversely  as  the  availabil- 
ity of  its  energy.  With  this  particular  hay.  it  would  have  been  nec- 
essary to  use  an  amount  containing  9.894  therms  of  metabolizable 
energy.  With  the  timothy  hay  used  in  an  earlier  experiment,  how- 
ever. 02.9  per  cent  of  whose  metabolizable  energy  was  found  to  be 
available,  corresponding  to  the  line  DG  in  figure  1.  it  would  have 
been  necessary  to  use  a  quantity  containing  only  5.590-M).029  = 
8.888  therms,  represented  in  the  figure  by  CKr.  in  order  to  supply 
the  requisite  available  energy  and  secure  maintenance.  On  the  other 
hand,  with  a  coarser  forage  having,  e.  g..  an  availability  of  only 
45  per  cent,  represented  by  DH,  it  would  have  been  necessary  to 
supply  5.590-f-0.45= 12.420  therms  of  metabolizable  energy,  repre- 
sented in  the  figure  by  the  line  Oil.  Just  as  was  illustrated  pre- 
viously in  the  case  of  the  dog.  while  the  real  requirement  of  energy 
for  the  vital  processes  remains  unchanged  the  amount  of  feed  nec- 
essary for  maintenance  is  variable,  depending  upon  the  availability 
of  its  energy. 

If  with  Zuntz  we  regard  the  increased  katabolism  consequent 
upon  taking  feed  as  representing  energy  expended  in  its  digestion 
and  assimilation,  we  may  state  the  case  in  a  slightly  different  way. 
We  may  compare  the  work  thus  done  to  the  work  of  placing  the  fuel 
under  a  factory  boiler.  If  this  is  done  by  means  of  power  derived 
from  the  same  boiler,  it  is  evident  that  the  farther  the  fuel  has  to 
be  moved  and  the  greater  the  amount  of  incombustible  waste  which 
it  contains,  the  larger  will  be  the  fraction  of  the  total  boiler  power 
required  simply  to  keep  the  fire  going  and  the  less  the  proportion 
available  for  running  the  factory.  So  in  the  body,  the  greater  the 
amount  of  energy  which  must  be  expended  on  the  food  in  order  to 
prepare  it  for  its  functions  in  the  body  the  less  is  the  proportion  of 
its  energy  which  is  available  for  carrying  on  the  physiological 
processes. 

RELATION    OF    MAIXTENAXCE    REQUIREMENT    To    LIVE    WEIGHT. 

Before  taking  up  the  specific  maintenance  requirements  of  farm 
animals,  it  is  necessary  to  consider  the  influence  of  size  and  weight 
upon  the  maintenance  requirement. 


RELATION    OF    MAINTENANCE    TO    LIVE    WEIGHT.  37 

That  large  animals  katabolize  more  matter  and  produce  more  heat 
than  smaller  ones  requires  no  special  proof.  Experiment  shows, 
ho\vever,  that  the  difference  is  not  proportional  to  size  or  weight, 
but  that  small  animals  have  a  relatively  more  intense  metabolism 
than  large  ones,  the  amount  being  approximately  proportional  to  the 
body  surface,  which,  of  course,  is  relatively  greater  in  the  smaller 
animal.  The  existence  of  such  a  relation  was  surmised  by  various 
writers,  but  we  are  indebted  to  Kubner1  for  the  first  quantitative 
investigation  of  this  question.  He  determined  the  fasting  katabolism 
of  six  dogs  whose  weights  ranged  from  3  to  24  kilograms.  With 
the  addition  of  earlier  experiments  by  Voit  on  a  still  larger  dog. 
the  average  results  were  as  follows,  the  total  katabolism  being  ex- 
pressed in  terms  of  computed  energy. 

Relation    of  faxtiny   katnltolixin    to    irciylit    and    t<>   surface — ItHbncr  and    Voit. 


No.  of  animal. 

j      Live 
weight. 

Katabolism 
per  kilo- 
gram, live 
weight. 

Katabolism 
per  square 
meter  of 
body 
surface. 

I   . 

Kilos. 
30.  06 

Calories. 
36.66 
40.91 
45.87 
46.20 
65.16 
64.79 
88.25 

Calories. 
1.046 
1,112 
1,207 
1.097 
1,183 
1.120 
1.214 

II   

23.71 

Ill                

'        19.  20 

IV  

17.70 

V  

9.  51 

VI           

6.  44 

VII           

3.10 

While  not  mathematically  constant,  the  ratio  between  the  fasting 
katabolism  and  the  surface  shows  a  close  approximation  to  uni- 
formity, and  the  same  fact  has  been  verified  by  a  considerable  num- 
ber of  subsequent  experiments.  Moreover,  it  has  been  shown  -  to 
be  approximately  true  not  only  of  animals  of  the  same  species,  but  of 
animals  ranging  in  size  from  man  to  domestic  fowls,  and  including 
also  cold-blooded  animals.  A  recent  investigation  by  Kettner  3  upon 
13  guinea  pigs  furnishes  a  striking  illustration  of  this  general  uni- 
formity. 

Ivubner  explains  the  apparent  dependence  of  the  fasting  katabolism 
on  body  surface  as  the  consequence  of  the  loss  of  heat  from  the  body 
due  to  the  cooling  action  of  the  environment,  which  would  naturally 
be  proportional  to  the  surfacjp.  The  fact,  howtver,  that  not  incon- 
siderable variations  have  sometimes  been  observed  indicates  that 
other  factors  than  the  elimination  of  heat  are  concerned,  and  appar- 
ently the  true  cause  lies  deeper.  Not  merely  the  heat  production  but 
all  the  important  physiological  activities  of  the  body,  including  the 
expenditure  of  energy  in  locomotion,  seem  to  be  proportional  to  the 


1  Zc-itsehrift  fiir  Biolojrio,  vol.   1!>.  p.  r>:\r>. 

-E.  Voit.      Zoitsrlirift   fiir   Kioloirio.   vol.   41.   p.    11.".. 

3  Archiv  fiir   (Anatomic1  und  i    Physiologic.   100!>,  p.  447. 


38  MAINTENANCE    EATIOXS    OF    FARM    ANIMALS. 

body  surface  rather  than  to  the  weight,  while  the  fact  that  the  same 
law  holds  true  for  cold-blooded  animals,  which  assume  the  tempera- 
ture of  their  surroundings  and  which,  therefore,  are  subjected  to  no 
demand  for  heat,  points  in  the  same  direction.  Apparently  we  have 
here  a  general  biological  law  of  which  the  proportionality  between 
heat  production  and  body  surface  is  one  expression. 

The  internal  work  of  the  animal,  however,  as  measured  by  the  fast- 
ing katabolism  or  the  fasting  heat  production,  constitutes,  as  we  have 
seen,  its  maintenance  requirement.  The  maintenance  requirements  of 
animals  of  different  sizes,  therefore,  especially  of  those  of  the  same 
species,  are  proportional  to  their  surfaces. 


COMPUTATION  OF  RELATIVE  UODY   .SURFACE. 


Few  actual  determinations  of  the  body  surface  of  animals  have 
been  made  and  almost  none  for  farm  animals,  so  that  it  is  at  present 
impossible  to  express  with  accuracy  the  metabolism  of  the  latter 
animals  per  unit  of  surface.  For  purposes  of  comparison  between 
individuals  of  the  same  species,  however,  another  method  serves  to 
give  at  least  approximate  results.  It  is  a  familiar  geometrical  fact 
that  the  surfaces  of  two  solids  of  the  same  shape  (i.  e.,  similar  figures 
in  the  geometrical  sense)  are  proportional  to  the  two-thirds  powers 
of  their  volumes.  By  regarding  all  animals  of  the  same  species  as 
of  the  same  shape  and  also  as  having  the  same  specific  gravity,  so 
that  their  weights  are  proportional  to  their  volumes,  it  is  a  very 
simple  matter  to  compute  their  relative  surfaces  and  the  correspond- 
ing maintenance  requirements.  For  example,  a  steer  weighing  583 
kilograms  was  found  to  have  a  computed  fasting  katabolism  (i.  e.. 
maintenance  requirement)  of  8.671  therms.  A  steer  weighing  500 
kilograms,  other  things  being  equal,  would  have  a  maintenance  re- 
quirement in  proportion  to  its  smaller  surface.  The  latter  would  be 
to  the  surface  of  the  larger  animal,  approximately,  as  (500) §  is  to 
(583)s  and  the  maintenance  requirement  would  therefore  be  8.G71 

x(  — 73  )3  =  7.878  therms.     In  this  way  it  i.-  a  simple  matter  to  com- 
\ooo/ 

pute  the  relative  maintenance  requirement.-  of  different  individuals 
without  the  necessity  of  expressing  them  per  unit  of  surface. 

Of  course,  such  a  comparison  i.->  only  approximately  correct.  In 
the  first  place,  it  may  be  presumed  that  there  are  differences  in  the 
specific  gravity  of  different  individuals,  although  it  may  be  doubted 
whether  these  difference"-  are  MiiTiciently  great  to  be  of  much  sig- 
nificance in  this  connection.  Moreover,  different  animals  are  not  of 
the  same  shape.  The  young  animal  differs  in  conformation  from  the 
«>lder  one,  and  the  beef  steer  and  the  dairy  cow,  for  example,  are  far 
from  being  geometrically  similar.  It  would  be  of  much  interest  to 
determine  the  relation  of  surface  to  weight  in  different  species,  types, 
and  ages  of  domestic  animals,  but  lacking  such  determinations  the 


MAINTENANCE   RATIONS   OF    CATTLE.  39 

method  of  computation  above  outlined  may  probably  be  assumed  to 
give  a  fair  approach  to  the  truth  and  is  at  any  rate  the  only  one 
available. 

THE    MAINTENANCE    RATIONS    OF    FARM    ANIMALS. 

In  endeavoring  to  formulate  the  maintenance  rations  of  farm 
animals  it  is  important  to  have  a  clear  conception  of  the  nature  of 
the  problem  and  to  distinguish  between  its  physiological  and  its 
economic  aspects.  The  physiological  conception  of  the  maintenance 
requirement  is  the  amount  of  energy  required  to  carry  on  the  abso- 
lutely necessary  vital  processes  in  a  state  of  the  most  complete  rest 
possible.  It  is  the  least  amount  on  which  life  can  be  sustained; 
the  physiological  minimum ;  the  base  line  for  comparison.  In  actual 
practice,  no  such  state  of  complete  rest  can  be  maintained  for  any 
length  of  time.  There  is  necessarily  superadded  to  the  minimum 
physiological  requirement  the  energy  expended  in  a  variety  of  ways, 
but  especially  in  the  numerous  minor  muscular  movements  which  are 
unavoidable  in  the  waking  state,  which  may  be  summarized  under 
the  term  incidental  work.  Some  of  the  factors  of  this  incidental 
work  are  discussed  on  subsequent  pages.  Physiologically,  this  addi- 
tional energy  is  expended  for  production ;  the  animal  is  doing  work 
on  its  surroundings.  Economically,  however,  the  work  done  is  of 
no  value  and  the  energy  required  to  do  it  is,  therefore,  from  that 
point  of  view,  a  part  of  the  cost  of  maintenance.  In  practice,  of 
course,  it  is  not  the  physiological  but  the  economic  requirement  which 
is  of  importance.  The  latter  will  necessarily  be  more  or  less  variable 
according  to  the  individuality  of  the  animal  and  the  conditions 
under  which  it  is  maintained,  as  will  appear  in  the  following  dis- 
cussion, and  statements  of  maintenance  requirements  and  rations 
should  therefore  indicate  to  such  a  degree  as  is  possible  the  conditions 
to  which  they  are  intended  to  apply. 


The  maintenance  requirements  of  cattle  have  been  more  exten- 
sively studied  than  those  of  other  species  and  it  will  be  convenient 
to  take  them  up  first,  using  the  data  also  as  a  means  of  illustrating 
the  principles  involved  and  the  methods  of  investigation  employed. 

The  estimate  of  the  maintenance  ration  of  cattle  long  current 
and  still  occasionally  cited  was  based  upon  the  investigations  of 
Henneberg  and  Stohmann  l  in  1858.  According  to  their  results,  a 
1.000-pound  steer  required  for  maintenance  about  8.10  pounds  of 
digestible  organic  matter  per  day.  equivalent  to  about  14.3  therms 
of  metabolizable  energy.  In  view  of  the  rather  high  stable  tem- 

1  P.eitrace  zur  Begriiudung  einer  rationelleu  Fattening  cler  WiedrrkJunT,  Heft  I, 
pp.  17-188. 


40 


MAINTENANCE    RATIONS    OF   FARM   ANIMALS. 


perature  in  these  experiments,  however,  Wolff 1  when  formulating 
his  well-known  feeding  standards  increased  this  amount  to  9.1  pounds 
digestible  organic  matter,  equivalent  to  about  15.9  therms  of  meta- 
bolizable  energy.  Numerous  subsequent  experiments,2  however, 
showed  quite  clearly  that  this  estimate  was  considerably  too  high 
but  without  affording  a  sufficient  basis  for  its  correction,  and  it  is 
only  since  1898  that  really  satisfactory  data  have  been  secured. 

One  general  method  of  experimentation  has  already  been  illus- 
trated in  the  computation  on  pages  34-35  of  the  maintenance  require- 
ment of  a  steer.  In  brief,  it  consists  of  comparing  the  losses  of  body 
energy  by  the  animal  when  fed  two  different  amounts  of  the  same 
feed  or  combination  of  feeds,  each  being  less  than  the  maintenance 
ration,  and  computing  from  the  difference  the  amount  of  energy 
required  for  simple  maintenance. 

Investigations  by  Armsby  and  Fries3  include  eight  trials  with  three  different 
animals  substantially  upon  this  plan.  In  the  later  experiments  of  the  series 
a  correction  was  made  for  differences  in  live'  weight  in  the  different  periods 
of  each  experiment  and  for  differences  in  the  amount  of  time  spent  standing 
and  lying,  the  results  being  computed  to  12  hours  standing.  The  results  here 
given  for  the  earlier  experiments  have  been  corrected  in  the  same  manner 
and  therefore  differ  somewhat  from  those  originally  reported.  The  follow- 
ing tabulation  of  the  results  shows  also,  for  comparison,  the  percentage  avail- 
ability of  the  metabolizable  energy  of  the  feed  and  likewise  the  maintenance 
ration  expressed  in  terms  of  metabolizable  energy.  The  results  in  every  case 
have  been  computed  to  a  uniform  live  weight  in  proportion  to  the  two-thirds 
power  of  the  weight.  It  is  to  be  noted  that  the  experiments  are  upon  coarse 
fodder  (clover  and  timothy  hay)  exclusively,  and  that  the  animals  were  not  fat. 

Maintenance  requirements  <in<1  rations  of  steers — .\rmxlty  and  Fries. 


Years. 

Animal. 

Available  energy 
for  maintenance. 

Percent- 
age 
availa- 
bility of 
metabo- 
lizable 
energy. 

Metabolizable  en- 
ergy   for    main- 
tenance. 

Feed. 

Per  500 
kilograms 
live 
weight. 

Per  1,000 

pounds 
live 
weight. 

Per  500 

kilograms 
live 
weight. 

Per  1,000 
pounds 
live 
weight. 

1903         

I 
I 
A 
]! 
A 
B 
A 
H 

Tlurms. 
f.  4S3 
7  Si  2 
ti  fV49 

(',  077 
il  SCO 
5  ISf, 
(i  931 

Thtrmx. 
G.  07»> 
7.321 
6.  231 
7.  05s 
5.  095 
(i.  378 
4.860 
6.  4U6 

Pa  ant. 
50.88 
80.  24 
60.51 
55.  21 
[57.05] 
[56.  50] 
57.05 
5(i.50 

Tlitrmn. 
12.  742 
9.  73G 
10.9S8 
13.  f42 
10.  (\52 
12.  046 
9.  090 
12.  207 

Th(rms. 
11.912 
9.124 
10.297 
12.  784 
9.982 
11.288 
8.  519 
11.4U7 

Clover  hav. 
Do. 
Timothv  hav. 
Do." 
Do. 
Do. 
Do. 
Do. 

1904 

1905 

190.5.           

1900 

1900 

1907 

1907  

\verage  of  all 

(1  CA.5 

f..2l  14 

59.  24 

11.395  •       10.079 
11.G32         10.901 

11.447         10.728 

Average,    omitting 
1904. 
Average,  1905-1007.. 

(i  523 

i1,.  -,:n 

6.113 

C,.  121 

of,.  21 
57.14 

1  LandwirtschaftlicliP  Filttprunirslehiv.  I'd  ed..   1S77.  pp.   !•'!'-'  and   r.Ki. 

2  The    Maintenance    Untion    of    Cattle,    Pennsylvania    Experiment     Station    P.nllolin    41'. 
pp.    12-21. 

::  I'.uivau  of  Animal  Industry.  Unlit-tins  74,  101.  and  ll'K.  The  results  reported  in 
r.uil-tin  No.  .".1  can  not  be  computed  directly  in  this  way  because  the  ration  included  a. 
small  fixed  amount  of  linseed  meal. 


MAINTENANCE  RATIONS   OF   CATTLE. 


41 


Omitting  the  results  of  the  year  1904,  which  are  obviously  too  high  both  as 
regards  the  maintenance  requirement  and  the  percentage  availability,  we  ob- 
tain the  following  averages  in  round  numbers : 


Available 
energy. 

Metaboliz- 
able 
energy. 

Per  500  kilograms  live  weight  

Therms. 
G.  52 

Therms. 
11  63 

J'er  1,000  pounds  live  weight  .... 

0.11 

10  90 

The  variations  from  these  averages  which  occur  in  individual  cases  illus- 
trate the  fact,  already  pointed  out,  that  the  economic  as  distinguished  from 
the  physiological  requirement  may  vary  considerably  with  different  animals 
and  under  different  conditions. 

The  experiments  just  cited  are  the  only  ones  thus  far  reported  in 
which  this  precise  method  of  determining  the  maintenance  require- 
ment in  terms  of  available  energy  has  been  followed.  In  the  major- 
ity of  investigations  the  effort  has  been  to  feed  as  nearly  an  exact 
maintenance  ration  as  possible,  making  a  correction  for  the  small 
gains  or  losses  by  the  animals,  and  the  results  of  these  experiments 
have  usually  been  expressed  in  terms  of  metabolizable  energy. 

By  far  the  most  exact  and  satisfactory  experiments  of  this  sort,  as  well  as 
the  earliest,  are  those  reported  by  Kellner  from  the  Moeckeru  Experiment 
Station1  in  1894  and  1S9G,  in  which  the  gain  or  loss  of  protein  and  fat  (nitro- 
gen and  carbon  balances)  was  determined  by  means  of  a  Pettenkofer  respira- 
tion apparatus.  In  these  experiments  the  feed  consisted  exclusively  of  coarse 
fodder,  viz,  meadow  hay,  or,  in  two  instances,  a  mixture  of  clover  hay  and 
oat  straw.  In  six  cases  out  of  the  eight  the  respiration  experiments  showed  a 
small  gain  of  protein  and  fat  by  the  animal ;  that  is,  the  ration  was  somewhat 
above  the  maintenance  requirement.  For  example,  the  gains  by  ox  A  on  meadow 
hay  and  the  computed  equivalent  amounts  of  energy  were: 


Material      Equivalent 
gained.          energy. 


Protein . 
Fat... 


Grams. 
37.2 
140.8 


Thcrmf. 
0.211 
1.338 


Total 


In  later  investigations  by  Kellner,  out  of  100  units  of  metabolizable  energy 
of  meadow  hay  supplied  in  excess  of  the  maintenance  requirement,  only  4?> 
were  recovered  in  the  protein  and  fat  gained  by  the  body.  To  produce  the  gain 
observed  in  this  experiment,  therefore,  may  be  computed  to  have  required 
1.549-K).43=o.602  therms  of  metabolizable  eneriry  and  the  ration  must  have  con- 
tained this  amount  in  excess  of  the  maintenance  ration.  The  following  calcti- 


1  Die  Landwirtschaftlichen  Versuchs-Stationen,  vol.  44,  p.  ."70;  vol.  47,  p.  310;  vol.  5:;, 
pp.    G-1G. 


42  MAINTENANCE    RATIONS    OF    FARM    ANIMALS. 

lation.   therefore,   shows  the  amount  of  metabolizable  energy  of  meadow  hay 
which  was  necessary  for  the  maintenance  of  the  animal : 

Therms. 

Energy   of  feed 32.177 

Energy  of  feces 11.750 

Energy  of  urin 1.945 

Energy  of  methane 2. 114 

Energy  of  total  excreta__  _ 15.  809 


Metabolizable  energy  of  ration 16.368 

Metabolizable  energy  equivalent  to  gain ___     3.602 


Metabolizable  energy  for  maintenance 12.  706 

This  method  of  computing  the  metabolizable  energy  necessary  for  maintenance 
is  obviously  the  same  in  principle  as  that  employed  in  Armsby  and  Fries's 
experiments,  differing  only  in  the  fact  that  the  comparison  is  made  on  amounts 
of  feed  exceeding  the  maintenance  ration.  Kellner's  results,  however,  can  not 
be  made  the  basis  of  a  direct  computation  of  the  available  energy  required  for 
maintenance,  since  it  appears  probable  that  a  larger  percentage  of  the  energy 
of  hay  is  available  below  the  point  of  maintenance  than  is  utilized  for  gain 
above  it.1 

In  two  cases  (ox  B  and  ox  IV)  the  rations  were  less  than  the  maintenance 
ration  and  the  animals  lost  more  or  less  protein  and  fat.  In  computing 
these  experiments  Kellner,  in  accordance  with  the  ideas  then  generally  ac- 
cepted, simply  added  the  energy  equivalent  to  the  loss  of  tissue  to  the  total 
metabolizable  energy  of  the  feed  to  obtain  the  maintenance  ration.  It  is  evi- 
dent, however,  from  what  has  subsequently  been  learned  regarding  the  avail- 
ability of  metabolizable  energy,  as  outlined  in  the  foregoing  paragraphs,  that 
if,  for  example,  ox  B  lost  tissue  equivalent  to  1.49S  therms  it  would  have 
required  more  than  this  amount  of  metabolizable  energy  in  the  food  to  make 
good  the  loss,  the  quantity  necessary  depending  upon  the  availability  of  the 
energy.  Of  the  latter  we  have  no  determinations  for  this  particular  ration,  but 
for  purposes  of  computing  a  correction  we  may,  perhaps,  assume  it  to  be  the 
same  as  that  found  by  Armsby  and  Fries  for  timothy  hay,  viz.  about  57  per 
cent.  On  this  assumption  the  equivalent  amount  of  metabolizable  energy  which 
would  have  had  to  be  supplied  to  reach  the  maintenance  ration  of  ox  B 
would  have  been  1.498-H).57=2.62S  therms,  a  difference  of  1.130  therms.  For  ox 
IV  the  corresponding  correction  is  only  0.740  therm. 

Making  these  slight  changes  in  Kellner's  original  figures  for  these  two 
animals  for  the  sake  of  uniformity,  his  results  are  as  follows: 

1  Compare  Bulletin  liiS,  liureau  of  Animal  Industry,  p.  59. 


MAINTENANCE    RATIONS    OF    CATTLE. 
Maintenance  rations  of  oxen — Kcllncr. 


43 


Live 

weight. 

Stable 
tempera- 
ture. 

Maintenance  ration 
(metabolizable  energy). 

Per  head. 

Therms. 

11.075 
17.  900 
12.  7U» 
15.861 
13.284 
14.  457 
11.771 
15.213 

Per  500 
kilograms. 

Per  1,000 
pounds. 

Thin  animals: 
Ox  V  

Kilos. 
002.  1 
011.5 
019.  8 
022.  H 
1132.  1 
032.  4 
044.0 
071.7 

°  C. 
14.7 
15.9 
15.9 
14.9 
14.7 
15.0 
14.8 
10.5 

Therm*. 
10.310 
15.  709 
11.000 
13.701 
11.352 
12.302 
9.944 
12.  480 

Therms. 
9.0C8 
14.721 
10.365 
12.  840 
10.639 
11.585 
9.  320 
11.702 

Ox  1$ 

Ox  A 

Ox  IV... 

Ox  III 

OxII 

Ox  VI 

Ox  XX     . 

Average  

14.  124 
13.  575 

12.110 
11.003 

11.355 

10.  874 

Average,  omitting  ox  15  

Fat  animals: 
Ox  1 

748.0 
750.  0 

858.0 

15.9 
15.2 
16.1 

23.  449 

19.  385 
22.  102 

17.93 
14.79 
15.  40 

10.80 
13.  80 
14.49 

Ox  B  ....                           

Ox  3  

Average 

21.0.50 

10.00                15.05 

The  observed  maintenance  ration  of  ox  15  is  notably  larger  than  that  of  the 
other  animals.  This  animal  refused  to  lie  down  during  the  respiration  experi- 
ments and  presumably,  therefore,  the  result  obtained  with  it  is  abnormally  high. 

Omitting  this  result,  the  maximum,  minimum,  and  average  maintenance 
rations  per  1,000  pounds  live  weight  were: 

Metabolizablc  energy  required  for  maintenance  of  cattle  per  1,000  pounds  lire 

weight — Kelt  net: 


Thin  animals: 

Maximum. 

Minimum. 

Average. .. 
Fat  animals: 

Maximum. 

Minimum. 

Average... 


Per  1.000 
pounds 

live 
weight. 


Therms. 
12.84 
9.32 

10.  87 

It',.  80 
13.  80 
15. 05 


If  we  are  justified  in  assuming,  on  the  basis  of  Armsby  and  Fries's  results. 
that  approximately  •"  per  cent  of  the  metabolizahle  energy  of  these  rations 
was  available,  then  the  foregoing  amounts  of  metaboli/able  energy  are  equiva- 
lent to  the  following  amounts  of  available  energy: 


Per  1.000 

Per  500 

pounds 

kilograms 

1  i  ve 

live 

weight. 

weight. 

For  thin  animals: 

Thfrms. 

Therms. 

7  T^ 

7.81 

.").:?! 

5.  67 

\  verago  

0.  20 

6.  61 

For  fat  animals: 

9.  58 

10  22 

N  41' 

8.58 

9  15 

44 


MAINTENANCE   RATIONS    OF   FARM    ANIMALS. 


Both  the  averages  and  the  range  of  the  results  obtained  by  Kellner  and  by 
Armsby  and  Fries  for  thin  cattle  on  coarse  fodder  show  a  remarkably  close 
agreement.  The  results  upon  fat  cattle  will  be  considered  on  subsequent  pages. 

In  addition  to  the  respiration  experiments  just  considered,  a  num- 
ber of  live- weight  experiments  upon  the  maintenance  ration  of  cattle 
have  been  reported. 

Such  trials  were  made  by  the  writer  at  the  Pennsylvania  Experiment  Sta- 
tion *  in  1892  to  1897,  the  feed  being  either  chiefly  or  entirely  coarse  fodder. 
The  live  weight  was  taken  daily  during  relatively  long  periods  and  the  nitrogen 
balance  was  also  determined,  and  from  these  data  an  approximate  computation 
of  the  loss  of  fat  was  attempted.  The  amount  of  methane  excreted,  and  the 
corresponding  loss  of  metabolizable  energy,  was  calculated  from  the  total  carbo- 
hydrates digested.  Computing  the  final  results  on  the  same  assumptions  as  in  the 
Moeckern  experiments,2  the  results  of  4  experiments  each  on  3  animals  weighing 
from  400  to  500  kilograms,  computed  per  500  kilograms  live  weight,  were: 

Metabolizable  encryy  in  maintenance  rations  of  steers — ArniNLi/. 


Ration. 

Per  500  k 
Steer  1. 

ilograms  li 
Steer  2. 

ve  weight. 
Steer  3. 

Chiefly  or  entirely  coarse  fodder: 
Experiment  1  ,  1892-93  

Therms. 
14.  23 
13.61 
12.  92 
13.03 

Therms. 
[17.09] 
13.56 
12.  87 
12.  76 

Therms. 
13.69 
12.40 
12.  73 

[17.77] 

Experiment  II  1892-189-1 

Experiment  VI,  1894-95                                                          

Experiment  VII,  1894-95                                              

Averages  (omitting  results  in  brackets)                                   

13.45 
11.72 

13.06 
9.  15 

12.94 
10.70 

Largely  grain: 

Assuming,  as  before,  that  about  57  per  cent  of  the  metabolizable  energy  was 
available,  and  omitting  the  two  apparently  exceptional  results,  the  maximum, 
minimum,  and  average  results  are: 


Ration. 

;  Metabolizable  energy. 

Available  energy. 

Per  500 

kilograms 
live  weight. 

Per  1,000 
pounds 
li  ye  weight. 

Per  500 
kilograms 
live  weight. 

Per  1.000 
pounds 
live  weight. 

Coarse  fodders: 
Maximum  

Therms. 
14.23 

Therms. 
13.34 
11.62 
12.32 

!).  S6 

Therms. 
8.11 
7.117 
7.  .50 
6.00 

Tl,enns. 
7.  60 
1.  f>2 
7.  0-2 
5.02 

12.40 

13.15 

Largely  grain   

10.52 

The  results  on  coarse  fodders  are  materially  higher  than  those  of  the  respira- 
tion experiments  just  cited,  but  Hie  method  is,  of  course,  much  less  accurate. 

Ilaecker3  reports  determinations  of  the  maintenance  rations  of  dry  cows  made 
in  three  successive  years  and  in  which  three  different  animals  were  used.  In 
these  experiments  the  niHrionts  digested  were  determined  directly  and  the 
sufficiency  of  the  ration  judged  of  from  the  live  weight  and  appearance  of  the 
animals.  Uesults  obtained  by  Kellner1  and  by  Armsby  and  Krles5  show  that 

1  Pennsylvania    Kxperiment    St.-ition.    Miilli'tin   -12. 

-'This  differs  somewhat  from  (he  m«'(h<>d  of  computation  followed  it!  the  original  report 
of  the  experiments. 

3  Minnesota   Kxperim"nt   Station.    Mullet  in   7!>. 

*  Hie   Landwirtschaftliehen    Vcrsuchs-Stal  ioneii.    vol.   5:1,   pp.   4-10-14.'. 

•"  Mureau  of  Animal   Industry,  Mulletins  ,"].  74.   101,  and  1:.'S. 


MAINTENANCE    RATIONS    OF    CATTLE. 


45 


the  metabolizable  energy  does  not  vary  greatly  from  l.G  therms  per  pound  (3.5 
therms  per  kilogram)  of  total  digestible  organic  matter,  even  in  rations  differing 
widely  as  to  the  kinds  of  feed  used.  From  (he  data  regarding  the  digestible 
matter  of  the  rations,  therefore,  the  equivalent  amounts  of  ruetabolizable  energy 
may  be  estimated  on  this  basis.  Computing  the;  results  per  1.0()0  pounds  in  pro- 
portion to  the  two-thirds  power  of  the  live  weight,  instead  of  directly  as  does 
Haecker.  the  results  are  as  follows: 


Maintenance  nit  if  tint  of  <lnj  ro/c.s- — llaeckcr. 


.  ,.„                Average 

Metabolizal 

)le  energy. 

Cow.                       Your.              live               Sn'Hv!                Kind  of  feed. 
wi»>'ht-         weight 

Per  head. 

I'er  1  .000 
pounds  live 
weight. 

Pounds.         j'oHiid. 
\lice                                   '    I89(i  97                   SOS                     0     Corn  fodder 

Therms. 

7  92 

Therms. 
9  13 

Belle                                     1K9U-97               1  010                    n 

9  21  j 

9  19 

A  verage                           .                          .-                         .        .        

9.  l(i 

Bell"                                       1897-9S               1,072                n  27    1  Corn  fodder,  beets, 

/           10.  lf> 

9.71 

Lottie..                               1S97-9S                  700                 .27   f    and  oil  meal 

7.01 

S.  S3 

Lottie                                     1S98-99                   757                    l'>     Not  stated 

S  9t> 

10  75 

A  verage                           .                         ...                                .                   .   

9.  7C, 

Average  of  all 

9  51 

i 

In  i  ho  first  year's  experiments  the  amount  of  digestible  protein  fed  was  small 
and  the  condition  and  appearance  of  the  animals  were  not  satisfactory.  In 
the  second  and  third  years  the  rations  were  richer  in  protein,  a  slight  gain 
in  live  weight  was  made,  and  the  condition  of  the  animals  was  entirely  satis- 
factory at  the  close  of  the  experiment.  Since  some  gain  was  made  in  the 
second  and  third  years  the  amount  consumed  was  naturally  somewhat  larger 
than  the  tirst  year.  The  proportion  of  grain  to  coarse  fodder  in  the  rations 
is  not  stated,  but  the  results  of  the  digestion  trials  indicate  that  it  must  have 
been  small.  If  we  assume  GO  i>er  cent  availability,  the  computed  available 
energy  of  the  rations  per  1.000  pounds  live  weight  is: 

Therms. 

Maximum--  G.  4.~. 

Minimum •">.  3<> 

Average  of  all ">.  71 

The  results  as  thus  computed  run  materially  lower  than  those  obtained  at 
Moeckern  and  at  the  Pennsylvania  station,  in  spile  of  the  fact  of  a  gain  in  live 
weight. 

Evvard1  fed  three  yearling  steers  for  GO  days  and  one  for  :'>(>-  days  on  rations 
so  adjusted  and  varied  as  to  very  exactly  maintain  their  live  weight,  the  average 
daily  gain  or  loss  being  practically  negligible.  The  experiment  in  the  case 
of  the  first  three  animals  followed  a  30-day  period  in  which  a  submaintenance 
ration  was  fed  and  the  animals  were  therefore  only  in  medium  condition." 

The  rations  fed  differed  from  those  of  the  exj>eriments  previously  quoted  in 
•  •ontaining  a  much  larger  proportion  of  grain,  consisting  of  4  parts  by  weight 
of  alfalfa  hay  and  10  parts  of  mixed  grain.3  Kvvard  computes  the  available 

'Thesis  for  degree  of  M.   S..   University  of  Missouri.   1000. 

-The  animals  graded  in  the  maintenance  period  as  follows:  Xo.  500.  common:  No.  fi'.ts, 
common  :  No.  506.  good  to  medium  ;  Xo.  505,  medium. 

3  Eight-ninths  corn  chop  and  one-ninth  old  process  linseed  meal. 


46 


MAINTENANCE    RATIONS    OF    FARM    ANIMALS. 


energy  of  the  rations  consumed  from  the  data  given  in  Bulletin  71  of  the  Penn- 
sylvania station  with  the  following  results: 

Maintenance  rations  of  yearling  steers — Evvard.     (First  experiment.) 


Estimated  available 

energy  per  day. 

No.  of 
animal. 

of  experi- 
ment. 

live 
weight. 

Per  head. 

Per  1,000 
pounds  i 
live 

1 

weight. 

Days. 

Pounds. 

Therms. 

Therms. 

590 

60    |             608 

5.  63    '           7.  85 

598 

60                  461 

3.  85                C.  45 

596 

60                   404 

4.34     '            7?  25 

595 

362                  009     i            5.83 

8.09 

1  Computed  in  proportion  to  the  two-thirds  power  of  the  live  weight. 

In  addition  to  the  uncertainty  attaching  to  such  live-weight  experiments,  as 
well  as  to  the  fact  that  the  available  energy  was  estimated,  there  is  also  a  special 
difficulty  in  determining  the  true  maintenance  requirement  of  growing  animals, 
which  will  be  referred  to  later.  Nevertheless,  the  results  appear  to  agree  fairly 
well  with  those  obtained  in  the  respiration  calorimeter  experiments. 

The  metabolizable  energy  of  the  rations,  also  computed  from  the  data  given 
in  Bulletin  71  of  the  Pennsylvania  station,  is,  on  the  other  hand,  lower  than 
fhat  found  in  either  the  Pennsylvania  or  the  Moeckern  experiments,  although 
agreeing  well  with  Haecker's  results  on  dry  cows.  viz.  per  1.000  pounds  live 
weight : 

Therms. 

No.    590 10.42 

No.   598 8.  57 

No.  590  _  !>.  03 


Average. 


Evvard's  first  three  animals  were  also  fed  a  maintenance  ration  of  the  same 
feeds  in  the  same  proportions  for  120  days  after  having  been  previously  fed 
heavier  rations  for  127  days,  during  which  No.  500  receive;!  about  one-fourth  of 
full  feed,  No.  59X  about  one-half,  and  No.  590  full  feed.  The  results  of  this 
second  maintenance  period  are  summarized  in  the  following  table: 

Mdintcnuii'-c  ration*  of  i/fdiiinif  xlcrrx — Krvunl.      (Second  experiment.) 


Estimated  available 

1 

energy 

per  day. 

No.  of 

animal. 

Length 
mi  nl. 

Average 
live 
weight. 

Per  head. 

!    Per  1,000 
pounds 

i 

weight.1 

Days. 

1'tiuml*. 

Thtrms. 

Thrrmt. 

500 

120 

701  i 

0.47 

8.15 

508 

120 

<i(>5 

(i.  44 

S.  45 

596 

120 

860 

9.  »>«> 

10.62 

1  Computed  in  proportion  to  the  two-thirds  power  of  the  live  weight. 


MAINTENANCE    EATTONS    OF    CATTLE. 


47 


The  data  contained  in  the  foregoing  pages  may  be  summarized  in 
the  following  table  showing  the  maximum,  minimum,  and  average 
maintenance  rations  in  various  experiments.  Armsby  and  Fries's 
results,  as  already  noted,  have  been  corrected  to  1'2  hours  standing. 
No  statement  of  the  amount  of  time  passed  standing  and  lying. 
respectively,  is  given  in  the  reports  of  the  other  experiments. 

Dailtl  maintenance  rat  hum  of  cattle  i>er  I.OO't  pimmlx  lire  wcif/Iit. 


Investigators. 

Condition 
of  animals. 

Num-   Num- 
ber of    bcr  of 
uni-     single 
msils.    trials. 

Metaboli/able  energy. 

Available  energy. 

Maxi- 
mum. 

Mini- 
mum. 

Aver- 
age. 

Maxi- 
mum. 

Mini- 
mum. 

A  ver- 
age 

Armsby  and  Fries.  . 
Kellner 

Thin.  .  . 
do 

3            7 
7             7 
3             3 
3            10 

Therms. 
12.  78 
12.84 
10.80 
13.34 

10.98 

Therms. 
8.52 
9.32 
13.  80 
11.62 

8.  57 

8.83 
,y   .-,7 

Therms. 
10.90 
10.  87 
15.  05 
12.  32 

9.  80 

9.51 
!1  .r,4 

Thcrrnx. 
7.0G 

7.  32 
9.  58 
7.  TO 

0.  20 

0.  45 

7.  S.") 

Therms. 
4.80 
5.31 

7.75 
0.  02 

4.88 

.5.  30 
'i.  45 

Tlifrmx. 
0.  11 
0.20 

8.  58 
7.02 

.5.  02 

5.71 
7.18 

8.09 

Do. 

Armsbv  (coarse  fod- 
der)." 
Armsby      (  in  u  c  h 
grain). 
Haecker  
Evvard,  00-day  ex- 
periment. 
Evvard,  302-day  ex- 
periment. 
Evvard,  second  ex- 
periment. 

Average  of  all   ex- 
periments. 
Average  of  respira- 
tion experiments. 

Fat  .  .  . 

Thin  

.  .  .    do 

...do... 
do 

3  !           5 

10.  75 
10  42 

do  

Partly  fat- 
tened. 

/Thin... 

;  ; 

so        sn 

f!              fi 

in        14 

10.74 

10.02 

7.  81 

8.  1.5 
>t.8G 

9.  07 

fS.Si 

8  M 

13.  S.'/ 

S.  51         10.  50 

\  Fat 

Thin  

12.  84 

8.  ,ril 

in.  80 

7.   ;.' 

.',.  W 

<;.  in 

The  foregoing  results  justify  the  statement  that  the  maintenance 
ration  of  thin  cattle,  expressed  in  terms  of  available  energy,  ranges 
in  general  from  5  to  7.5  therms  per  1.000  pounds  live  weight,  aver- 
aging a  little  above  0  therms.  The  maintenance  ration  of  fat  animals 
appears  to  be  distinctly  greater  than  that  of  thin  ones. 

It  should  be  noted  that  the  term  available  energy  is  used  in  the 
sense  defined  on  pages  20-22.  as  determined  by  a  comparison  of  ex- 
periments upon  submaintenance  rations.  This  available  energy  is 
not  necessarily  identical  with  the  energy  values  in  terms  of  which 
the  values  of  feeding  stuffs  and  the  requirements  of  animals  have 
been  expressed  by  Kellner  and  others  (compare  Farmers'  Bulletin 
;Uf>),  since  his  results  were  obtained  by  a  comparison  of  super- 
maintenance  (productive)  rations.  Such  scanty  data  as  are  now  on 
record  seem  to  indicate  that  the  two  are  substantially  the  same1  in 
case  of  concentrated  feeds, "but  that  the  available  energy  of  coarse 
feeds  below  maintenance  may  be  greater  than  their  productive  values 
above  the  point  of  maintenance.  If  this  should  prove  to  be  the  case, 
then  evidently  an  estimated  requirement  of  <>  therms  of  Kellner's  pro- 
duction values  will  give  a  maintenance  ration  ample  for  practical 
purposes,  but  which  will  be  a  somewhat  too  large  deduction  to  make 
in  estimating  the  productive  part  of  the  ration. 


48  MAINTENANCE    RATIONS    OF    FARM    ANIMALS. 


Data  regarding  the  maintenance  rations  of  sheep  are  less  com- 
plete than  for  those  of  cattle.  No  experiments  are  on  record  in 
which  the  requirement  of  available  energy  has  been  directly  deter- 
mined, and  but  few  respiration  experiments  have  been  made.  Most 
of  the  recorded  data  are  based  upon  live-weight  experiments. 

In  186T-CS  Hermeberg  and  his  associates  J  conducted  a  series  of  respiration 
experiments  upon  two  mature  sheep  receiving  approximately  a  maintenance 
ration  of  meadow  hay.  Two  digestion  experiments,  including  determinations  of 
the  nitrogen  balance,  were  made  with  each  of  the  animals.  During  each  of 
these  digestion  experiments  three  respiration  experiments  were  made  upon  the 
two  animals  together.  The  results  of  these  determinations  vary  so  little  that 
their  average  is  sufficient  for  our  present  purpose.  Estimating,  as  in  some  of  the 
experiments  on  cattle,  that  each  kilogram  of  digestible  organic  matter  contains 
approximately  3.5  therms  of  metabolizable  energy,  and  further,  that,  as  in  the 
case  of  Kellner's  steers,  43  per  cent  of  the  metabolizable  energy  of  the  feed 
could  be  stored  up  in  the  form  of  gain  of  flesh  and  fat,  the  following  computa- 
tion per  day  and  head  may  be  made  : 

Maintrwtnrc  ration  o/  shcey — Ilcnncbcrg  and  StohmauH. 

Live  weight,  exclusive  of  wool kilograms.-  45.4 

Digestible  organic  matter  per  day grains..  539.1 

Gain  by  animal : 

Protein do 7.  95 

Fat  _. do 13.  75 

Therms. 
Metabolizable  energy  of  ration  0.5391X3.5 1.887 

Metabolizable  energy  equivalent  to  gain  : 

Therm. 

Protein.  0.00795  kilo.X5.7 0.0453 

Fat.  0.01375  kilo.  X9.5  __  .  130i; 


.  1759     -H).  43-_          .  409 


Metabolizable  energy  fur  maintenance 1.478 

The  foregoing  ration  is  equivalent  to  1.574  therms  per  50  kilograms,  or 
1.475  therms  per  100  pounds,  computed  in  proportion  to  the  two-thirds  power  of 
the  live  weight. 

In  1S72  Ilenneberg,  Fleischer,  and  Miiller2  began  a  series  of  respiration 
experiments  upon  sheep  in  which  wheat  glulen  was  added  to  a  basal  ration  of 
hay  and  ground  barley.  The  basal  ration  of  the  first  period  proved  to  be  but 
slightly  greater  than  the  maintenance  ration.  Making  the  same  calculations  as 
before,  but  assuming  that  50  per  cent  of  the  metabolizable  energy  of  the  ration 
might  serve  for  the  production  of  gain,  since  a  portion  of  the  ration  consisted 
of  grain,  we  have  the  following: 


1  Nriip   Rpitriltfp.   i-tr.,   pp.    OR-2S6. 

2  .TahrpsboTiflit    d'-r  Auriculturchpniic,   vol.    10-17,    II.   145. 


MAINTENANCE   RATIONS   OF    SHEEP. 

Maintenance  ration  of  sheep — Henncberg,  Fleischer,  and  Mullcr, 

Live  weight kilograms__ 

Digestible  organic  matter  per  day grams__ 

Gain  by  animal : 

Protein   grains. _ 

Fat grains__ 


49 


Metabollzable  energy  of  ration  0.50294  X  3.;" 

Metabolizable  energy  equivalent    to  gain — 

•  Therm. 

Protein,  0.00104X5.7 ___  0.0110(5 

Fat,  0.0430  X9.5__  .4142O 


34.  20 
502.  94 

1.94 
43.00 

Therms. 
1.  970 


.42520 -HO. .',()__        .851 


Metabolizal)le  energy  for  maintenance _  1.119 

This  result  is  equivalent  to  1.441  therms  per  r»0  kilograms  or  1.350  therms  per 
100  pounds  live  weight. 

Hagemann,1  from  the  results  of  a  digestion  and  metabolism  experiment  and  of 
42  short8  respiration  periods  with  the  Zimtz  type  of  apparatus  on  a  mature 
sheep  averaging  50.33  kilograms  live  weight,  computes  an  approximate  energy 
balance  which  may  be  put  in  the  following  form,  assuming  that  50  per  cent  of 
the  surplus  metabolizable  energy  of  the  mixed  ration  might  be  recovered  as 
gain: 

Maintenance  ration  of  xhceji — Hagctnann. 


Feed: 
Alfalfa  hay  

Therms. 
2.181 

Therms. 

Corn  meal  

1.524 

Uneaten  

0  009 

Excreta: 
Feces  .... 

1  332 

Urine  

146 

Gain:                                                                                                                 Therm. 
1.44  grams  protein  0.  008 

46.20  erams  fat  ...                                                                                             .  439 

Maintenance. 


.914 
1.304 


3.705 


3.705 


In  addition  to  the  foregoing  experiments  there  are  a  number  of  digestion 
experiments  by  Wolff,  in  which  the  live  weight  of  the  animals  was  approxi- 
mately maintained.  In  1871 3  two  series  of  exi>eriments  were  made  upon 
the  relative  digestive  power  of  three  breeds  of  sheep  for  an  approximate 
maintenance  ration.  A  comparison  of  the  live  weights  of  the  animals  is  possible 
only  for  the  second  series,  in  which  the  ration  consisted  of  clover  hay  and 
potatoes.  The  total  organic  matter  digested  j>er  day  and  bead  and  the  average 
live  weights  at  the  beginning  and  end  of  the  experiment  were  as  given  in  the 

1  Archiv  ftir  (Anatomic  und  i   riivsiolo£jp,  1SOO,  Suppl.,  p.   13S. 

-  Usually   not    cxroofliiiR  "0  to  40  minute*. 

3  Landwirtschaftllchc  .Tahrbiicher,  vol.  1.  p.  533. 

S4S9°— Bull.  143—12 1 


50 


MAINTENANCE   RATIONS   OF   FARM   ANIMALS. 


table,  which  also  shows  the  metabolizable  energy  equivalent  to  the  digested 
organic  matter  (3.5  therms  per  kilogram),  both  per  head  and  per  50  kilograms 
live  weight,  computed  in  proportion  to  the  two-thirds  power  of  the  latter.  The 
average  result  is  equivalent  to  1.G34  therms  per  100  pounds  live  weight. 

Maintenance  rations  of  sheep — Wolff. 


Breed. 

Number 
of 
animals. 

Live  weight.1 

Digested 
organic 
matter  per 
day  and 
head. 

Equivalent  metaboliz- 
able energy  per  day. 

Initial. 

Final. 

Per  head. 

Per  50  kilo- 
grams live 
weight. 

Electoral  merino 

{      1 

I 

i             5 

{             6 

Kilos. 

39.85 
42.05 
49.85 
47.45 
67.  55 
59.05 

Kilos. 
39.20 
40.50 
49.50 
47.20 
66.20 
59.70 

Grams. 
345.  35 
342.  34 
537.  97 
523.  24 
680.  43 
620.  38 

Therms. 
1.209 
1.198 
1.883 
1.831 
2.382 
2.171 

Therms. 
1.414 
1.361 
1.891 
1.898 
1.963 
1.936 

Natives 

Southdowns  . 

Average 

1.779 

1.744 



1  Average  of  5  or  6  consecutive  days. 

In  1892-93  Wolff1  made  a  series  of  experiments  with  sheep  on  the  influence 
of  salt  upon  digestibility.  In  the  first  two  periods  of  this  series  an  approxi- 
mate maintenance  ration  of  1.000  grams  of  meadow  hay  per  day  and  head 
was  fed.  Since  the  salt  was  found  not  to  affect  the  digestibility  of  the  feed, 
we  may  use  the  results  of  the  two  periods  as  a  basis  for  computing  the  main- 
tenance ration.  The  average  live  weights  per  head  were  as  follows: 


January 
2,  3,  and  4. 

February 
5,  6,  and  7. 

Sheep  No  1 

42.9 

44.0 

Sheep  No.  2 

43.8 

42.8 

Sheep  No.  3  

42.8 

44.5 

Sheep  No.  4 

42.2 

42.0 

Average. 

42  9 

43.3 

The  feed  consumption  was  uniform  with  all  the  animals  and  the  percentage 
digestibility  showed  but  very  slight  variations,  so  that  we  may  regard  the 
average  of  the  eight  trials  as  representing  approximately  the  maintenance 
ration.  The  average  amount  of  organic  matter  digested  per  day  and  head 
was  476.28  grams.  Reckoning,  as  before,  3.5  therms  of  metabolizable  energy 
per  kilogram,  this  corresponds  to  1.C507  therms  per  head,  equivalent  to  1.841 
therms  per  50  kilograms  or  1.725  therms  per  100  pounds  live  weight,  computed 
in  proportion  to  the  two-thirds  power  of  the  latter. 

Wolff2  has  also  computed  the  digestible  matter  in  the  rations  consumed  by 
sheep  in  a  number  of  the  earlier  experiments  by  Henneberg.  The  average  of 
six  rations  which  appeared  amply  sufficient  for  maintaining  the  live  weight  of 
the  animal  was,  per  head  : 

Kilograms. 

Live  weight i 40.05 

Organic  matter  digested .  500 

Equivalent  metabolizable  energy--  therms__     1.981 


1  Landwirtschaftliche  .Tahrbiiohor,  vol.  :i.r>,  p.  175. 

-  Ernahrung  dor  Landwirtschaftliche  Nutzlierc,  pp.  410-419. 


MAINTENANCE    RATIONS    OF    SWINE. 


51 


Computed  in  the  usual  way,  this  is  equivalent  to  2.J-JOO  therms  per  GO  kilo- 
grams. This  is  a  much  higher  result  than  was  obtained  in  any  of  the  other 
experiments,  and  in  view  of  the  fact  that  the  digestibility  of  the  rations  was 
estimated  and  that  the  feed  was  of  a  somewhat  varied  character  it  seeuis  per- 
missible to  omit  this  result  from  consideration. 

The  results  of  the  experiments  cited,  omitting  the  ones  last  men- 
tioned, may  be  summarized  as  follows: 

DdiJii  in<iintcn(iii<-<'  r<iti<>nn  of  .s/icr/>. 


Metabolizable  energy. 

Kind  of  experiment,  and  investigator. 

Per  50  kilo-       Per  lOu 
grams  live    pounds  live 
weight.          weight. 

Respiration  experiments: 
Ilennelxjrg  and  Stohmann 

Therms.    \     Thermn. 
1.574                1.475 

IIennel>erg,  Fleischer,  and  MiiMcr 

1.  441  I              1.  358 

llagemanu  .... 

1.304                1.222 

A  verage   .  .   . 

1.440                1.352 

Digestion  experiments: 
WollT,  1871.  0  experiments 

1.744                I.(i34 

Wolff,  1892-3,  8  experiments  

1.841  :              1.725 

Average     .    ... 

1.  793  !              1  080 

A  verage  of  all 

1  581                 1  4n:j 

It  is  of  some  interest  to  compare  this  average  maintenance 
ration  of  sheep  Avith  the  corresponding  results  for  cattle.  If  we 
assume  that  the  surfaces  exposed  by  these  two  species  are  roughly 
proportional  to  the  two-thirds  powers  of  their  live  weights,  the  cor- 
responding maintenance  ration  for  a  1.000-pound  steer  would 

be  1.483  x(  -  -  )§  —  0.885  therms  of  metabolizable  energy  as  com- 
pared with  an  average  of  10.50  therms  for  cattle.  While  such  a 
comparison  is,  of  course,  but  a  rough  approximation,  it  nevertheless 
seems  to  show  conclusively  that  the  metabolism  of  the  sheep  per 
unit  of  surface  is  distinctly  lower  than  that  of  cattle.  No  obvious 
reason  for  such  a  difference  suggests  itself.  That  it  can  hardly  be 
due  to  the  direct  effect  of  the  wool  in  diminishing  the  radiation  of 
heat  will  appear  from  a  discussion,  in  a  later  section,  of  the  influence 
of  external  temperature  on  the  maintenance  requirement. 

S  \VINK. 

Two  determinations  of  the  fasting  katabolism  of  swine  have  been 
reported  by  Meissl.  Strohmer,  and  Lorenz.1  The  experiments  were 
made  with  the  respiration  apparatus,  no  calorimetric  determinations 
being  carried  out. 

Computing  the  energy  katnbolized  by  the  use  of  Knbner's  factors  for  the  en- 
ergy corresponding  to  the  nitrogen  and  carbon  excreted,  the  writer2  obtained 

1  Zeitschrift  fur  Bioloj,'ie.  vol.  22.  p.  6.'i. 
-  Principles  of  Animal  Nutrition,  p.  452. 


52 


MAINTENANCE    RATIONS    OF    FARM    ANIMALS. 


the  figures  contained  in  the  third  column  of  the  following  table.  Kellner  '  has 
recomputed  the  results,  using  the  exact  figures  for  the  carbon,  nitrogen,  and 
energy  content  of  the  flesh  of  swine  which  were  obtained  by  Kohler,  with  the 
results  shown  in  the  last  column. 


Fn*ti>i</  katabolism  of 


Mcissl,  Strohtnrr.  dixl   Lorcnz. 


Live 
weight, 


i  Fasting  katabolism. 


!  Annsbv.  !  Kellner. 


Experiment  V.. 
Experiment  VI. 


Kilos.        Therms.      Ttitrms. 
140  2.  GOT  !          2.737 

120  2.291  I          2.385 


Computing    Kelhier's    figures    to    uniform    live   weight    in    proportion    TO   the 
surface  we  have : 


!    Per  50 
kilo- 
grams. 

Per  100 
pounds. 

Therms. 
Experiment  V  i        1.  377 

Therms. 
1.290 

ExDeriment  VI  ...                                                                                                                         1.  333 

1.249 

Average 1 . 355 


1.270 


These  figures,  according  to  the  principles  enunciated  in  the  foregoing  pages, 
may  be  regarded  as  representing  the  available  energy  required  for  mainte- 
nance. No  other  direct  determinations  of  this  requirement  appear  to  have  been 
made. 

In  addition  to  the  foregoing,  a  number  of  live-weight  experiments 
have  been  reported. 

Dietrich  2  determined  the  amount  of  feed  required  by  growing  pigs  to  maintain 
their  live  weight  at  different  stages  of  growth.  The  trials  were  made  when  the 
animals  reached  approximately  the  weights  of  50,  100,  150.  and  200  pounds,  4 
animals  being  used.  The  digestibility  of  the  ration  fed  -,\\  the  weight  of  lf>o 
pounds  was  also  determined.  The  actual  average  ;ini*>iiiits  ot  feed  required  per 
dav  and  head  were  as  follows: 


<it 


Period. 

,Vv(U-!i«e 
live 

;•'•'.><!    ri'(iiiiri'(i    fo 
nunce. 

,'oni           Mi'l- 
rneal          (llins.'s. 

I                                                  

V.}  (V_' 

0.  i:>             o.  15 

'.IX.  7.;) 

.40               .4(1 

Ill 

i  r>  i  .  _>f> 

.  so  !             .M) 

IV 

201  v 

I 

,,      ...                                                   ,      .....           v 

-    i        i             i  •   • 

-Wisconsin   l^xpcriment   Station,   10th   K«-p-»rt,   1S')'I, 


Skim 
milk. 


•nindx 


1.2 
1.6 
1.0 


MAINTENANCE   RATIONS   OF   SWINE. 


53 


Assuming  the  composition  of  the  feeding  stuffs  used  to  be  fairly  represented 
by  the  averages  given  in  Farmers'  Bulletin  22  (revised)  and  using  Jordan's 
digestion  coefficients  for  middlings,  oil  meal,  and  skim  milk,  and  Kellner's 
coefficients  for  corn  ineal,  the  writer  has  computed  the  digestible  nutrients 
contained  in  the  rations  consumed  with  the  results  shown  in  the  following  table. 
The  metabolizable  energy  of  the  rations  has  been  computed  from  the  amount  of 
digestible  nutrients,  using  the  factors — 

Caloriod  per  gram. 

Digestible  protein 4.1 

Digestible  nitrogen-free  extract 4.2 

Digestible  crude  fiber 3.5 

Digestible  ether  extract S.  8 

Computed  digestible  nutrients  and  metabolizable  energy  per  day — Dietrich's 

experiments. 


Period  . 

Digestible  nutrients  per  head. 

Metabollzable  energy. 

Protein. 

Carbohy- 
drates. 

Fat. 

Per  head. 

Per  50  kilo-       Per  100 
grams  live  j  pounds  live 
weight.    ;     weight. 

Pounds. 
0.005 

.  12!) 

.204 

.  205 

Pounds. 
0.241 
.  501 
1.  033 
1.  159 

Pounds. 
0.012 
.028 
.0.00 

.  o:.7 

Therms. 
0.028 
1.  415 
2.  5.50 
2.817 

Therms.    '     Therms. 
1.009  ;             1.002 
1.523  i              1.427 
2.009  ,              1.939 
1.8S5                1.700 

II 

III 

IV                   .            

Taylor '  re-ports  quite  similar  experiments  with  animals  weighing  respec- 
tively 50,  100,  and  150  pounds.  Computed  in  the  same  manner  as  the  previous 
experiments,  the  results  are  as  follows: 

Maintenance  rations  of  sirim-  ut  different  agi'x — Tai/lfn: 


I... 
ill. 
v.. 


Perio<!. 


Average 

live 
weight. 


Feed  required  for  mainte- 
nance. 


Corn 

meal. 


Oil 
meal. 


Pounds.  Pounds.  \  Pounds.  \  Pounds. 

52. 1  0. 4S  |  0. 24  ',            0.  OS 

103.5  1.14  !  .57  '              .19 

157.0  1.20  .00  i              .20 


ilii/i'.ytible  nutrient*  anil  Hwtubfiliznblc  energy  i><:r  day — Taylor's  >-.r- 
periments. 


Digestible  nutrients  per  head. 


Metabolizable  energy. 


Perlocis. 

Protein. 

Carbohy- 
drates. 

Fat. 

Per  head. 

Per  50  kilo- 
grams live 
weight  . 

Per  100 
pounds  live 
weight. 

I 

Pounds. 
0.  0% 

Pounds. 
0.434 

Pounds. 
0.025 

Therm*. 
1.  105 

Therm*. 
1.S21 

Therms. 
1.  707 

III          

.233 

1.030 

.0.58 

2.  li  IX 

2.  730 

2.  55S 

V  

.240 

1.0S3 

.001 

2  753 

2.  174 

2.  037 

1  Wisconsin  Experiment  Station  Report,  1901.  p.  07. 


54  MAINTENANCE   RATIONS   OF   FARM   ANIMALS. 

Carlyle1  reports  the  average  daily  food  for  maintenance  of  12  brood  sows  for 
eight  weeks  after  weaning  their  pigs  as  follows: 

Pounds. 

Average  live  weight 306 

Feed  per  day  and  head  : 

Corn 1.49 

Shorts 1.  49 

Oil  meal .50 

Skim  milk 6.90 

The  computed  digestible  nutrients  and  energy  of  the  above  ration  are: 

Pounds. 
Digestible  protein 0.  654 

Digestible  carbohydrates 2.  307 

Digestible  fat .  117 

Equivalent  metabolizable  energy  :  Therms. 

Per  head 6.079 

Per  50  kilograms  live  weight 3.077 

Per  100  pounds  live  weight 2.884 

In  a  preliminary  report  of  experiments  upon  pig  feeding.  Dietrich  2  estimates 
the  maintenance  ration  of  growing  pigs  per  100  pounds  live  weight  to  be: 

Pounds. 

Digestible  crude  protein 0.10 

Digestible  carbohydrates .  40 

Digestible  fat .  04 

This  ration,  using  the  same  factors  as  before  for  the  metabolizable  energy, 
is  equivalent  to  1.181  therms  per  50  kilograms  or  1.107  therms  per  100  pounds 
live  weight. 

The  foregoing  results  show  a  wide  range  in  the  apparent  food 
requirement  for  the  maintenance  of  live  weight.  In  general,  the 
lower  results  seemed  to  have  been  reached  with  the  younger  animals. 
This  may  be  due,  however,  to  the  fact  that,  as  will  be  shown  in  a 
subsequent  paragraph,  the  maintenance  of  live  weight  in  a  young 
animal  is  not  necessarily  synonymous  with  the  maintenance  of  its 
store  of  potential  energy.  If  we  omit  the  results  obtained  with  the 
50-pound  animals  and  also  omit  Dietrich's  results  at  the  Illinois 
Station,  since  his  experiments  seem  to  have  been  with  comparatively 
young  animals,  we  find  the  range  of  results  to  be  as  follows: 


Per  50 
kilo- 
grams. 

Per  100 
pounds. 

Minimum                         .                    .             .... 

Therms. 
1.523 

Therms. 
1.427 

Maximum  

3.077 

2.884 

2.243 

2.  102 

On   the  basis  of   respiration  experiments  by  Meissl  as  discussed 
by  Kellner,3  four  rations  consisting  of  not  dissimilar  feeds  showed 


1  Wisconsin    Experiment   Station,   Rulletin   104,   p.   Til.     ' 

2  Illinois  Experiment  Station,  Circular  1 2f>,  p.  110. 

3  Die  Erniihrung  dor  I.andwirtsehaftliche  Nutztiere,  5th  ed.,  p.  157. 


MAINTENANCE    RATIONS    OF    HORSES. 


55 


an  approximate  average  utilization  of  74.5  per  cent  of  the  meta- 
bolizable  energy  supplied  in  excess  of  the  fasting  katabolism.  If 
we  may  apply  this  percentage  to  the  average  of  the  foregoing  results 
regarding  maintenance,  we  may  compute  the  average  requirement 
of  available  energy  to  be  2.243X0.745  =  1.671  therms  per  50  kilo- 
grams, or  1.5G6  therms  per  100  pounds,  a  result  not  differing  very 
widely  from  the  figures  computed  on  a  previous  page  from  the  results 
of  experiments  on  the  fasting  katabolism,  but  with  a  very  wide 
range  of  variation  in  individual  cases. 


TIIK     HORSK. 


The  maintenance  ration  of  the  hor^e  has  been  the  subject  of  inves- 
tigation by  Zuntz  and  Ilagemann,  Wolff,  Miintz,  and  Grandeau  and 
Le  Clerc. 


/.I'.ViZ    AND    HAGEMANN'S     INVESTIGATIONS. 


Upon  the  basis  of  the  results  regarding  the  availability  of  energy 
for  the  horse,  which  have  been  described  on  pages  22-25,  Zuntz  and 
Ilagemann  J  compute  the  fasting  katabolism  of  the  horse  by  sub- 
stantially the  same  method  as  that  employed  on  pages  34-35  for  cattle. 

For  this  purpose,  they  use  those  rest  experiments  on  horse  III  in  which 
the  feed  consisted  of  oats,  hay,  and  straw.  From  the  results  of  the  respira- 
tion experiments  made  within  the  first  five  hours  after  feeding,  they  compute 
the  total  energy  kutabolism  per  day  in  the  manner  indicated  on  page  22,  and 
from  this  subtract  the  energy  expended  in  the  digestion  of  the  feed  (not 
including  the  work  of  mastication),  computed  as  shown  on  page  23.  The 
remainder,  of  course,  is  the  katabolism  due  to  internal  work,  together  with  any 
katabolism  resulting  from  a  possible  demand  for  heat  to  maintain  the  body 
temperature.  Their  results  may  be  tabulated  as  follows: 


Computed  fasting 


of 


\>a    <l<ii/   ami   Jio.nl  —  Zunt~   anil   Hagc- 


Feed. 

Fasting 

katabo- 

Live 

weight. 

Energy 
katafoo- 
llsm. 

Oats.   '  Straw. 

Hay. 

Work  of 
digest  ion. 

FastiiiR     1  ism  per 
kalabo-       square 
lism.     1  centime- 
ter hodv 

Season. 

surface. 

Grim- 

Kilos. 

Therms. 

Kilo*.      Kilos. 

Kilos. 

Thirms.      Therms. 

calories. 

Period  a  

428.  1 

12.541 

6              1             7 

X  403  '         4.  138 

80.7 

Winter. 

Period  6 

434.  1 

11.674 

6               1 

i) 

7  704           3.  970             76.  7 

Summer. 

Period  e  450.4 

12.  364 

(i               1 

6 

7  704           4.  WQ 

S7.9 

Winter. 

Period/  449.1 

11.783 

0              1 

4.75 

6  830 

4.  953 

93.  6 

Summer. 

Period  #       .              440.  1 

11.893 

6               1 

7  704 

4.  1S9 

SO.  2 

Winter. 

Period  n  448.  2 

11.407 

4.8          0            .V  1 

5  f)72           5.735            10S.  5 

Slimmer. 

Period  c  442.2 

12.  450 

0               0      1     10.  .5 

7  340           5.110             97.6 

Do. 

Period  No.  ll.Sc         434.  0 

11.021 

4.8           O.S  !       l.SS 

4  122           6.899            133.3 

W  inter. 

In  the  experiments  with  a  standard  ration  of  0  kilograms  of  oats, 
1  of  straw,  and  (5  (or  7)  of  hay.  the  average  computed  fasting  katab- 
olism for  the  three  winter  periods  i.-  4.320  therms,  while  in  the 


1  Loc.  cit.,  pp.  2.s:!-l'S4  and  4l!.">— IL'0. 


56  MAINTENANCE    RATIONS    OF    FARM    ANIMALS. 

single  summer  period  it  reaches  the  minimum  of  3.970  therms.  Zuntz 
and  Hagemann  consider  that  the  latter  represents  approximately 
the  minimum  requirement  for  internal  work  and  regard  the  higher 
figures  obtained  in  the  winter  experiments  as  indicating  a  stimula- 
tion of  the  heat  production  by  the  low  temperature  to  which  the 
animal  was  exposed.  The  notably  higher  results  obtained  with  the 
lighter  rations  they  ascribe  to  a  similar  cause,  viz,  that  the  heat 
arising  from  the  work  of  digestion  and  from  the  necessary  internal 
work  (fasting  katabolism)  was  insufficient  to  maintain  the  body 
temperature.  Accordingly,  they  regard  the  differences  shown  in  col- 
umn 8  of  the  foregoing  table  as  including  in  these  cases  not  only  the 
minimum  necessary  for  internal  work  but  also  an  expenditure  for 
heat  production.  In  other  words,  they  consider  that  the  critical  tem- 
perature (compare  p.  71)  for  the  horse  is  high  as  compared  with  that 
for  cattle,  and  the  critical  amount  of  food  small  (compare  p.  73). 
Earlier  experiments1  upon  another  horse  in  which  lighter  rations 
were  fed  confirmed  this  conclusion. 

On  the  average  of  the  8  most  satisfactory  experiments  out  of  12,  the  esti- 
mated total  katabolism  per  day  and  head  was  11.027  therms  upon  a  ration 
consisting  of  3.5  kilograms  of  oats.  0.5  of  straw,  and  2.5  of  hay.  Computed  in 
the  same  manner  as  in  the  foregoing  examples,  the  expenditure  of  energy  in 
the  digestion  of  this  ration  is  equal  to  3.7S2  therms,  which  leaves  a  remainder 
of  7.244  therms,  equivalent  to  140.3  gram-calories  per  square  centimeter  of  sur- 
face. This  is  a  higher  figure  than  any  of  those  contained  in  the  foregoing  table, 
although  the  total  katabolism  was  not  notably  different.  The  authors  conclude, 
therefore,  that  the  small  amount  of  heat  liberated  by  the  digestive  work  was 
compensated  for  by  an  increased  katabolism  of  body  tissue. 

From  a  balance  experiment  on  the  same  animal  in  the  respiration  apparatus 
cf  the  Gottingen  Experiment  Station  they  also  compute2  the  metabolizable 
energy  required  for  maintenance  by  subtracting  from  the  lotal  nutrients  di- 
gested the  fat  equivalent  of  the  protein  and  fat  gained  by  the  animal.  They 
thus  reach  a  maintenance  ration  per  500  kilograms,  live  weight,  of  3.205 
grains  digestible  nutrients,  equivalent  to  32.93  therms.  Their  final  conclusion 
<  loc.  cit.,  p.  420)  is  that  their  animal  required  per  head  at  least  11  therms,  or  per 
500  kilograms  live  weight  12.10  therms,  of  heat  to  maintain  his  body  tempera- 
ture. In  other  words,  this  is  the  minimum  of  metabolizable  energy  which  must 
be  supplied  in  a  maintenance  ration,  since  if  less  be  present,  even  although  the 
ration  supplies  the  requisite  amount  of  available  energy,  body  tissue  will  still 
be  katabolized  for  the  production  of  the  heat  necessary  to  maintain  the  body 
temperature. 

Computed  to  1,000  pounds  live  weight  in  proportion  to  the  two- 
thirds  power  of  the  latter.  Zuntz  and  Hagemann's  maintenance 
ration  is: 

Therms. 

Available  energy  for  internal  work 4.  OS 

Additional  required  for  heat  production...  7.  SO 


Total  metabolizable  energy  required 11.88 


1  Landwirtschaf tllchc   Jakrbiiclicr,    vol.    IS,    p.    1;    vol.    27,    Krgiiuzungs    Band    III,    pp. 
356-L>.->7. 

2  Ibid.,    p.    423-424. 


MAINTENANCE   RATIONS    OF    HORSES. 


57 


The  maintenance  requirement  as  measured  by  the  computed  fast- 
ing katabolism  is  notably  less  than  that  of  cattle.  The  same  criti- 
cisms which  have  been  made  of  Zuntz  and  Ilagemann's  conclusions 
as  regards  availability  are  also  applicable,  of  course,  to  his  compu- 
tation of  the  maintenance  requirement. 

WOLFF'S     INVESTIGATIONS. 

Wolff  has  also  determined  by  a  different  method  the  maintenance 
ration  of  the  horse  in  the  experiments  whose  results  as  regards 
the  available  energy  of  feeds  have  already  been  mentioned  on  page 
25.  As  there  noted,  the  amount  of  work  performed  by  the  horse 
was  adjusted  so  as  to  be  as  nearly  as  possible  in  equilibrium  with 
the  feed  consumed.  Wolff's  experiments  were  made  with  a  sweep 
powrer  arranged  to  serve  also  as  a  dynamometer.  The  actual  meas- 
urements of  the  \vork  performed,  except  in  the  later  experiments, 
proved  to  be  too  low ;  but  Wolff  believes  them  to  be  relatively  correct, 
so  that  the  ratio  between  the  work  as  measured  and  the  additional 
feed  required  to  produce  it  may  still  serve  as  the  basis  of  computation. 

In  the  experiments  of  18T7-1SS61  it  was  found  that  the  work  performed  in 
100  revolutions  of  the  dynamometer  required  the  addition  to  the  ration  of 
315  grams  of  digestible  nutrients.  It  is  important  to  note,  however,  in  view 
of  what  follows,  that  this  additional  digestible  material  included  no  digestible 
crude  fiber — that  is,  that  it  was  practically  derived  from  the  grain  added  in 
the  periods  of  heavier  work.  Subtracting  from  the  total  digestible  nutrients 
of  the  ration,  therefore,  an  amount  computed  on  this  basis  to  be  equivalent  to 
the  work  done  leaves  a  remainder  representing  the  nutrients  required  for  mainte- 
nance on  the  virtual  assumption  that  all  the  work  done  was  performed  at  the 
expense  of  nutrients  derived  from  the  grain.  The  results  of  these  computa- 
tions are  summarized  in  the  following  table: 

Maintenance  ration*  of  Jiorxex — Wolff,  /<S'?'?'-./.SW. 


Animal. 

Number       Total 
of  e.xperi-  ;     nutri- 
ments,         ents. 

Nutri- 
tive 
ratio. 

Live 

weight. 

Number 
of  revolu- 
tions. 

Equiva- 
lent nutri- 

Cllta. 

Mainte- 
nance 
ration 
by  (infer- 
ence. 

Horse  I  

Grams. 
4       (1,  30  >.  0 

1:5.79 

Kilos. 
521 

600 

Grama. 
1  .  S90 

Grams. 
4,410 

Horse  II: 
1881  82 

7       5,831.1 

1:6.64 

477 

540 

1,720 

4  111 

1882-83 

4       6,  748.  3 

1:0.37 

480 

fi62 

2,  ON  5 

4,0(i3 

1883-84  

6       5.920.2 

1:7.20 

457 

1,780 

4.  134 

17        ti.07S.  4 

l:(i.80 

47;i  • 

1.818 

4.  200 

Horse  III: 

1S81-82          .      .      . 

(')       5.313.8 

1:7.  lii 

454 

404 

1  ,  273 

4.041 

18S2-83  

(i       0,001.3 

!:('..  8.8 

4(.9 

<>3 

2.  1.12 

3.909 

1SS3-84 

5       5.734.8 

1:7.55 

•573 

.580 

1  .  S27 

3.908 

1885             

4       5.7(11.2 

1:7.57 

473 

1,811 

3.050 

Average 

21  '     5,717.8 

1  :  7.  29 

407 

501 

1,700 

3,952 

fiir  die  rationale   Fiit  toruui;  dos   I'fcnlos,    1SSO,   00-155;    Xcuo   noitraj. 
Landwirtschaftliche  Jahrbiicher,   vol.   16,   Erganzungs   Hand   III,   1-48. 


58 


MAINTENANCE    RATIONS    OF   FARM    ANIMALS. 


Computed  to  500  kilograms  live  weight  on  the  basis  of  what  Wolff  regards 
as  the  normal  weights  of  the  animals,  the  foregoing  maintenance  rations  are : 

Grams. 

Horse  I 4, 143 

Horse  II 4,  260 

Horse  III 4, 167 

A  series  of  similar  experiments  on  horse  III,  weighing  475  kilograms,  in  1885- 
86,1  computed  in  substantially  the  same  way,  gave  results  for  the  maintenance 
ration  agreeing  well  with  those  of  earlier  years,  viz : 

Maintenance  rations  of  a  horse — Wolff,  1885-86. 


Period. 

Per  head. 

Per  500 
kilo- 
grams. 

I... 

Grams. 
3,934 

Grows. 
4,141 

II  

3.984 

4,194 

Ill  and  V... 

4  001 

4  212 

Vllb  

4,094 

4,310 

VIII  

4  094 

4  310 

Average 

4  021 

4  232 

In  a  succeeding  period  (IX),  however,  in  which  hay  alone  was  fed,  a  de- 
cidedly higher  result  was  obtained,  viz,  4,357  grams  per  head,  or  4,586  grams 
per  500  kilograms. 

In  these  earlier  experiments,  in  accordance  with  the  views  then  prevalent, 
Wolff  regarded  the  so-called  nutrients  as  of  equal  value  whatever  their  source. 
The  experiment  with  hay,  just  mentioned,  however,  suggested  that  such  was  not 
the  case  and  this  suspicion  was  confirmed  by  later  investigations  which  clearly 
showed  the  superiority  of  the  digestible  matter  of  grain  over  that  of  hay. 
This  superiority  was  not  apparent  in  the  earlier  experiments  because  the  pro- 
portions of  grain  and  coarse  fodder  were  not  widely  different  in  the  several 
experiments,  the  coarse  fodder  furnishing  on  the  average  fully  one-half  of 
the  dry  matter  fed. 

This  difference,  suggested  by  the  experiment  on  hay,  was  demonstrated  by  a 
comparison  by  Wolff2  of  his  own  results  with  those  obtained  by  Grandeau  and 
Le  Clerc 3  in  experiments  upon  two  cab  horses  receiving  only  a  small  amount  of 
walking  exercise.  The  ration  used  by  the  latter  experimenters  consisted  of 
about  75  per  cent  of  grain  as  against  less  than  50  per  cent  in  Wolff's  experiments, 
and  from  it  Wolff  computes  an  average  maintenance  ration  per  500  kilograms 
of  3.626  grams  of  digestible  nutrients  as  compared  with  the  4,000  to  4,200  grams 
of  the  foregoing  table. 

Direct  experiments  by  Wolff4  likewise  show  that  the  digestible  nutrients  of 
concentrated  feed  (oats)  are  more  valuable  for  work  production  than  those  of 
coarse  feed  (hay).  The  experiments  were  made  in  the  manner  already  de- 
scribed, the  draft  being  uniformly  60  kilograms.  Although  (he  measurements 
of  the  work  actually  done  are  probably  incorrect,  it  may  be  assumed  to  have 
been  substantially  proportional  to  the  number  of  revolutions  of  the  dyna- 
mometer. A  ration  of  3  kilograms  of  hay  and  5.5  kilograms  of  oats  served  as 
the  basal  ration,  to  which  was  added  on  the  one  hand  4  kilograms  of  hay  and 


1  I.andwirfschaftliolH'  .Fahrhiicher,  vol.   1.'!, 

2  Iliid.,   pp.   7:5-81. 

3  L'Alimontation  du  Clioval  do  Trait,  188",  II,  86  and 

4  Loc.  cit,   pp.   84-95. 


I5and  III,  p.  32. 


MAINTENANCE    RATIONS    OF    HORSES. 


59 


on  the  other  14   kilograms  of  oats.     The  nutrients  digested  in  each  case  and 
the  equivalent  amounts  of  work  secured  were: 

\utricntn  equivalent  to  work — Wolff,  /,s<Stf-<S?'. 


Period. 

Ration. 

Digested. 

Equivalent 
work. 

Protein. 

Crude 
fiber. 

Grams. 
810.08 

422.74 

:  Nitrogen- 
free  extract. 

Kther 
extract. 

Total  (fat 
X  2.4). 

Mil... 
V. 

7  kilograms  hay,  5.5  kilo- 
grams oats  

Grams. 

822.58 

620.46 

Grams. 

3,889.04 

3,008.78 

Grnm.,1. 
180.72 

184.  78 

Grams. 
5,  973.  02 

4,501.13 

Revolutions. 
750 

350 

3  kilograms  hav,  5.5  kilo- 
grams oats  

VI  
V  

4  kilograms  hay  
Per  100  revolutions  

190.12 

393.  94 

821.18 

1.94 

1,412.49 
353.  12 

400 

3  kilograms  hay,   7   kilo- 
grams oats 

7,54.  52 
626.  46 

355.  24 
393.  94 

3.719.24 
3.008.46 

252.17 
1,84.  78 

.5,434.21 
4.561.13 

700 
350 

3  kilograms  hay,  5.5  kilo- 
grams oats.  .  .".  

1  .  5  kilograms  oats  
Per  100  revolutions  

128.00        -67.  .50 

050.  78 

07.39 

873.  08 
249.  45 

350 

1 

The  relative  value  of  the  digested  matter  of  hay  and  of  oats  for  work 
production  in  these  trials  was  thus  approximately  as  5:  7. 

The  digestible  nutrients  added  to  the  ration  by  the  oats  in  period  VI  in- 
cluded no  crude  fiber,  and,  as  the  table  shows.  24!)  grams  of  these  fiber-free 
nutrients  were  found  equivalent  to  100  revolutions  of  the  dynamometer  with 
a  draft  of  00  kilograms,  which  is  practically  equivalent  to  the  335  grams  per 
100  revolutions  with  TG  kilograms  draft  found  in  the  earlier  experiments 
(p.  57)  in  which  also,  as  was  noted,  the  additional  nutrients  were  practically 
fiber-free.  Of  the  digestible  nutrients  added  to  the  ration  in  the  form  of  hay 
in  period  i-IIl,  on  the  other  hand,  over  one-fourth  consisted  of  crude  fiber, 
and  in  this  case  353  grams  were  found  to  be  equivalent  to  100  revolutions 
of  the  dynamometer.  If,  however,  the  digestible  crude  fiber  be  omitted  in  this 
case,  it  appears  that  the  fiber-free  nutrients  of  the  hay  were  practically  equiv- 
alent to  those  of  the  oats,  255  grams  being  required  for  each  100  revolutions. 

As  noted  previously,  Wolff  recomputed  his  experiments  on  the  assumption 
that  the  crude  fiber  was  valueless,  and  obtained  results  expressed  in  terms  of 
fiber-free  nutrients  which  were  consistent  among  themselves  and  agreed  with 
those  obtained  by  (Irandeau.  The  following  table  contains  a  summary  of  the 
results  obtained  for  the  maintenance  ration  expressed  both  in  terms  of  total 
nutrients  (including  digestible  crude  fiber)  and  of  fiber-free  nutrients: 

Nutrient.?  for  maintenance  per  ~>00  kilogram*  lire  icciylit — Wolff. 


Experiments. 


Fjber.free 


Experiments  of  1881-1885: 

Horse  I 

Horse  II 

Horse  III... 


Average 


)"  xiieriments  of  1885-80 — Horse  III: 

Period  I 

Period  II 

Period  III  and  V 

Period  VII 

Period  VIII 

Period  IX.. 


Average. 


Grams.     , 

Grains. 

4.143  ; 

3.378 

4.2CO  j 

3.282 

4.107 

3.300 

4.190  | 

3.322 

4.141 

3,142 

4.191 

3.  3.53 

4.212 

3.413 

4.310  , 

3.549 

4.310 

3.490 

[4.586] 

3.335 

i  4.232 

3.430 

Omitting  period  IX. 


60  MAINTENANCE    KATIONS    OF    FARM    ANIMALS. 

Nutrients  for  maintenance  per  500  kilograms  live   weight — Wolff — Continued. 


Experiments. 

Including 
fiber. 

Fiber-free. 

Grandeau's  experiments: 
Horse  II  

Grams. 
3  636 

Grams. 
3  324 

Horse  III  

3,017 

c         3  32S 

Average  

3,  626 

3  326 

Experiments  of  1886-87: 
Period  I-III  

1,202 

3,342 

Period  IV  

4  150 

3  429 

Period  V  

3,792 

3  y>§ 

Period  VI.....  . 

3  738 

3  364 

Average 

3  971 

3  366- 

The  figures  inclusive  of  the  crude  fiber,  as  computed  by  Wolff,  evi- 
dently correspond  approximately  with  the  amounts  of  metabolizable 
energy  contained  in  various  mixed  rations  which  were  sufficient  for 
maintenance.  In  the  earlier  experiments,  and  in  those  later  ones  in 
which  approximately  equal  proportions  of  hay  and  grain  were  con- 
sumed, the  amount  is  approximately  4,200  grams  per  500  kilograms 
live  weight,  which,  using  Zuntz  and  Ilagemann's  factor  of  3.96 
calories  per  gram,  is  equal  to  10,032  calories.  In  the  later  experi- 
ments, in  which  a  larger  proportion  of  grain  was  fed,  the  total 
nutrients  required  for  maintenance  ranged  from  3.000  to  3,700  grains, 
equivalent  to  from  14,257  to  14,052  calories.  In  other  words,  the 
amount  of  metabolizable  energy  necessary  for  maintenance  varied 
with  the  proportion  of  coarse  fodder  present,  as  would  be  expected 
from  the  results  with  cattle  recorded  on  previous  pages. 

The  maintenance  ration  in  terms  of  metabolizable  energy,  us 
thus  computed,  is  comparable  with  that  estimated  by  Zuntz  and 
Ilngemann,  in  the  manner  explained  on  pages  55-50,  from  the  total 
heat  production  of  the  animal.  That  Wolff's  results  are  higher  is 
probably  due  to  the  relatively  larger  proportion  of  crude  fiber  in  his 
maintenance  rations,  since,  as  shown  on  page  57,  the  work  is  assumed 
by  Wolff's  method  of  calculation  to  have  been  done  at  the  expense  of 
the  nutrients  of  the  grain,  and  consequently  the  remaining  portion  of 
the  ration,  which  is  regarded  as  the  maintenance  portion,  was  rela- 
tively poorer  in  grain  and  richer  in  coarse  fodder. 

Zuntz  and  Ilagemann  '  attempt  to  estimate  the  difference  due  to 
the  latter  fact.  They  average  31  of  Wolff's  experiments,  divided 
into  two  groups,  viz,  those  on  light  and  on  heavy  work,  correcting 
the  actual  amount  of  work  done  for  the  loss  of  live  weight  and 
likewise  for  what  they  regard  as  Wolff's  error  in  his  estimate  of  the 
energy  expended  in  locomotion.  They  also  correct  Wolff's  estimate 


MAINTENANCE   RATIONS   OF   HORSES.  61 

of  the  energy  of  the  digested  matter  by  the  use  of  the  factor  3.90 
calories  per  gram  instead  of  4.1  calories  per  gram.  Their  compari- 
son of  the  two  groups  gives  them  by  difference  31  per  cent  as  the 
proportion  of  the  available  energy  of  the  digested  nutrients  which 
was  recovered  in  the  form  of  work,  a  percentage  corresponding  very 
closely  to  that  found  for  the  work  of  draft  in  their  experiments, 
viz,  31.4.  Upon  this  basis,  they  compute  in  each  group  the  amount 
of  nutrients  required  for  the  total  work  done  and  by  subtraction 
the  total  digestible  nutrients  required  for  maintenance. 

Their  results  for  an  animal  weighing  approximately  500  kilograms 
are  as  follows,  the  equivalent  metabolizable  energy  being  obtained 
by  the  use  of  Zuntz  and  Ilagemann's  factor  of  3. DC  calories  per  gram. 
The  average  does  not  differ  materially  from  that  computed  directly 
from  Wolff's  later  experiments. 

Total  Equivalent 
digestible  j  metaboliz- 
nutrients.  able  energy. 


Periods  of  light  work. 

Grams. 
!           3,776 

Therms. 
14.95 

Periods  of  heavy  work 

i            3,763 

14.90 

Average... 

3,770 

14.  93 

This  result  they  compare  with  that  obtained  by  them  in  a  balance 
experiment  with  a  respiration  apparatus  from  which,  as  noted  on 
page  5G,  they  compute  a  maintenance  ration  of  12.93  therms. 
Their  ration,  however,  contained  notably  less  crude  fiber  than  did 
Wolff's  rations,  the  differences  being  as  shown  in  the  following 
table,  which  includes  also  the  equivalent  digestive  work,  estimated 
by  Zuntz  and  Hagemann  at  2. 05  calories  per  gram : 


Difference  i  Equivalent 
in  crude        digestive 
fiber  fed.  work. 


Periods  of  li.^ht  work 
Periods  of  heavv  work . 


Subtracting  this  amount  from  the  average  computed  from  WolffV 
experiments  leaves  a  remainder  of  12.37  therms  as  the  metabolizable 
energy  which  would  have  been  necessary  for  maintenance  had  Wolff's 
rations  contained  no  more  crude  fiber  than  Zuntz  and  Hagemann's. 

Wolff's  experiments  afford  no  data  for  computing  in  terms  of 
available  energy  the  maintenance  requirement  in  the  sense  in  which 
this  term  is  used  by  Zuntz  and  Hagemann  and  in  the  discussion  of 
the  maintenance  requirements  of  cattle,  on  pages  33  to  35,  viz.  as 


62 


MAINTENANCE    RATIONS    OF   FARM   ANIMALS. 


equivalent  to  the  necessary  demand  for  internal  work.  Even  if  we 
follow  Wolff  in  regarding  the  energy  of  the  fiber-free  nutrients  as 
an  approximate  expression  of  the  available  energy,  his  computation 
of  the  fiber-free  nutrients  required  for  maintenance  simply  shows  the 
amount  of  available  energy  (in  this  sense)  present  in  a  maintenance 
ration,  but  gives  no  indication  of  how  much  of  this  may  have  been 
consumed  in  simple  heat  production. 

MU.NTZ'S    EXPERIMENTS. 

Muntz,1  in  1878-79,  attempted  to  determine  the  maintenance  ration 
of  the  horse  by  a  different  method,  viz.  by  starting  wTith  an  insufficient 
ration  and  gradually  increasing  it  until  an  equilibrium  between  food 
and  live  weight  was  secured.  His  experiments  were,  made  upon 
horses  of  the  Paris  Omnibus  Co.  whose  work  ration  was  known  from 
previous  experiments.  Upon  one-third  of  their  regular  working 
ration  four  horses  lost  in  from  one  to  one  and  a  half  months  an  aver- 
age of  1.02  pounds  per  day  and  head.  The  ration  was  then  increased 
to  one-half  of  the  work  ration.  Upon  this  nine  horses,  including  the 
four  used  in  the  previous  experiments,  gained  on  the  average  1.08 
pounds  per  day  and  head.  Upon  decreasing  the  ration  to  five- 
twelfths  of  the  work  ration,  six  other  horses  gained  0.46  pound  per 
day  and  head.  The  amount  of  total  organic  matter  consumed  by 
the  animals  is  recorded.  Estimating  from  this  the  total  digestible 
nutrients  and  computing  the  metabolizable  energy  of  the  latter  at 
the  rate  of  3.96  calories  per  gram,  the  last  two  rations  afforded  the 
following  results : 

Metabolizable  enerr/y  in  rations  of  hornet — M-iinl.z. 


Metabolizable     en- 

ergy. 

Average 
gain  in 
weight 
per  day. 

Average 
live 
weight. 

Digesti- 
ble nu- 
trients. 

Per  head. 

Per  1,000 
pounds 

live 

weight  . 

Kilos. 

Kilos. 

Grams. 

Therms. 

Therms'. 

One  half  of  work  ration 

+0.49 

54.5 

4.  102 

16.  24 

14.37 

Five-twelfths  of  work  ration            

+0.  19 

523 

3,417 

13.53 

12.  ;U 

•  MlAXUEAf    ANT)    MO    CLERC  8    RESULTS. 


Grandeau  and  Le  Olerc,2  in  addition  to  the  experiments  recorded 
in  connection  with  Wolff's  results,  fed  five  cab  horses  a  daily  ration 
of  8  kilograms  of  hay  during  a  total  of  14  periods  of  a  month  each 
(1  to  5  periods  for  each  animal),  during  each  of  which  the  digesti- 
bility of  the  ration  was  determined.  The  animals  had  only  a  small 

1  Annales  de  I'lnstitut   National  Axronomique.  Tomo  .1.   1S7S-79. 
2L'Alimentation  du  Chcval  do  Trait,  1883,  III. 


TRUE    MAINTENANCE    AND    LIVE-WEIGHT    MAINTENANCE. 


63 


amount  of  walking  exercise  daily.     The  following  are  the  results  of 
the  several  periods : 

M.ctal)0lizal)lc  energy  in  rations  of  hortscx — Grandeau  and  Le  Clcrc. 


Total 
digestible 
nutri- 
ents.1 

Equiva- 
lent ine- 
taboliza- 
ble  en- 
ergy. 

A  verage 
daily 
gain  or 
loss  of 
weight. 

Average 
live 
weight. 

Horse  30845  (No.  1): 
January  1884 

Grams. 
2  895  3 

Therms. 
11  467 

Kilos. 
0  19 

Kilos. 
394  9 

April,  1884  

2,351.9 

9.315 

+0.47 

379.2 

August.  1884  

2,795.5 

11.071 

+0.03 

365.  0 

September,  1884.  .  . 

2,927.8 

11.595 

1  —  0.  03 

366.3 

October,  1884  .   .   . 

2,  897.  1 

11.473 

3  0.00 

366.0 

Average     

2  773.5 

10.983 

+0  06 

374  3 

Horse  29475  (No.  2): 
November,  1883  .  .  . 

3  041.4 

12.  045 

+0  59 

423  6 

Horse  29466  (No.  2): 
May,  1884  

2,  470.  2 

9.784 

+0.42 

404.0 

June,  1884  

2,  909.  5 

11  523 

+0  13 

407.1 

July,  1884  

2,602.8 

10.  663 

+0.18 

410.6 

Average     

2  690.8 

10  656 

+0  94 

407  2 

Horse  29407  (No.  3): 
December,  1883  .... 

3  062  1 

12  128 

0  05 

413  9 

Horse  26925  (No.  3): 
March,  1884  

2,  726.  8 

10.799 

+0.82 

419.0 

June,  1884  

2  644  5 

10  473 

+0  27 

384.  3 

July,  1884  

2  719  4 

10  770 

0  00 

387.7 

August,  1884  

2,837.9 

11  238 

—0  01 

388.4 

Average  

2  732  2 

10  8^0 

+0  °7 

394  9 

1  Including  fat    X2.4. 

-Omitting  last  day  of  each  month. 

On  the  average  of  all  the  periods,  the  results  per  day  and  head 
were  as  follows : 

Total  digestible  nutrients  (fatX2.4  )  __  __grams__  2,7*3.7 

Equivalent    uietabolizable    energy,    at    3.90    calories    per 

gram therins__         1 1.  03 

Daily  gain  in  weight kilograms 0.19 

Average  live  weight do 393.  G 

The  foregoing  ration,  which  was  apparently  somewhat  more  than 
a  maintenance  ration,  is  equivalent  to  12.12  therms  of  metabolizable 
energy  per  1,000  pounds  live  weight.  This  is  materially  less  than 
was  obtained  in  Wolff's  experiments  and  about  the  same  as  that  found 
by  Zuntz  and  Hagemann  for  rations  containing  much  grain. 

TRUE   MAINTENANCE  AND   LIVE-WEIGHT    MAINTENANCE. 

The  maintenance  of  an  animal  in  the  strict  scientific  sense  signifies 
the  preservation  of  the  store  of  matter  and  of  potential  energy  con- 
tained in  the  body,  and  only  a  ration  which  effects  this  is  really  a 
maintenance  ration.  As  has  appeared  in  the  foregoing  pages,  how- 
ever, much  of  our  recorded  information  regarding  the  maintenance 


64  MAINTENANCE  RATIONS   OF   FARM   ANIMALS. 

ration  is  derived  from  experiments  in  which  the  sufficiency  of  the 
ration  was  judged  of  from  its  effect  in  maintaining  the  live  weight 
of  the  animal.  In  experiments  on  mature  animals  extending  over  a 
considerable  period  of  time,  it  is  unlikely  that  any  gross  error  is 
involved,  especially  if  determinations  of  the  nitrogen  balance  show 
the  protein  supply  to  be  adequate.  In  short  periods,  on  the  other 
hand,  and  especially  in  experiments  upon  young  animals,  the  live 
weight  is  a  notoriously  untrustworthy  guide.  The  general  reasons 
for  this  are  familiar,  but  in  young  animals  another  very  important 
factor  enters  into  consideration.  As  is  well  known,  the  tendency  to 
growth  is  one  of  the  most  marked  characteristics  of  young  animals. 
Waters 1  has  shown  that  this  impulse  to  increase  of  tissue  is  so  marked 
that  it  may  apparently  take  precedence  over  the  demand  for  main- 
tenance, so  that  an  animal  may  continue  to  increase  in  size  of  skeleton 
for  a  considerable  time  even  on  a  submaintenance  ration. 

Some  15  immature  cattle  were  fed  for  considerable  periods  on  ra- 
tions just  sufficient  to  maintain  their  live  weight.  Under  these  condi- 
tions the  animals  continued  to  growr  in  height,  in  depth  of  chest,  and 
length  of  head.  At  the  same  time,  however,  there  was  an  evident 
falling  off  in  the  amount  of  fat  tissue,  both  as  judged  by  the  eye  and 
as  shown  by  the  appearance  and  by  the  chemical  composition  of  the 
carcass.  Histological  studies,  too,  showed  a  reduction  in  the  size  of 
the  fat  cells,  and  analysis  of  the  adipose  tissue  showed  a  lower  fat  and 
higher  water  and  protein  content  than  in  check  animals.  What 
occurred  was  evidently  a  consumption  of  body  fat  to  supply  energy, 
while  at  the  same  time  an  approximately  equal  weight  of  protein  tis- 
sue was  produced  which,  on  account  of  the  relative!}7  low  energy  value 
of  protein  and  of  the  relatively  large  amount  of  water  accompanying 
it.  represented  a  much  smaller  quantity  of  energy  than  did  the  fat  tis- 
sue which  disappeared.  In  other  words,  the  rations  were  not  really, 
but  only  apparently  maintenance  rations.  It  is  perhaps  hardly  correct 
to  say  that  in  these  experiments  growth  was  maintained  at  the  ex- 
pense of  the  fat  of  the  tissues.  A  more  exact  statement  of  the  case 
would  be  that  the  increase  of  protein  tissue  and  water  masked  the 
loss  of  fat.  Presumably  this  effect  would  be  less  marked  in  more 
mature  animals,  in  which  the  true  maintenance  and  live-weight 
maintenance  would  doubtless  approach  each  other  closely  when  meas- 
ured over  long  periods. 

FACTORS  AFFECTING  THE  ENERGY  REQUIREMENT. 

The  results  of  the  experiments  upon  farm  animals  reported  on 
previous  pages  render  it  evident  that  the  actual  maintenance  require- 
ment, even  when  computed  to  a  uniform  weight  or  size,  is  more  or 

1  Soeioty  for  the  Promotion  of  Agricultural  Science,  Proccodinirs  of  IMMli  Annual  Moot- 
ing, p.  71. 


FACTORS   AFFECTING   THE   ENERGY    REQUIREMENT.  65 

less  variable.  For  example,  in  the  case  of  cattle,  for  which  the  most 
extensive  and  accurate  data  are  available,  the  range  of  the  energy 
requirement  per  day  and  1,000  pounds  live  weight  for  thin  animals 
in  those  experiments  which  are  apparently  the  most  accurate  is  4.9 
to  7.3  therms  available  energy  or  8.5  to  1-2.8  therms  metabolizable 
energy.  Several  causes  may  be  responsible  for  these  variations. 

MUSCULAR    ACTIVITY. 

Ill  considering  the  factors  of  the  fasting  katabolism  (p.  9).  atten- 
tion was  called  to  the  large  share  which  the  muscles,  and  especially 
the  voluntary  muscles,  have  in  the  heat  production  of  the  animal. 
Even  in  a  state  of  the  most  complete  rest  possible,  a  very  considerable 
share  of  the  total  katabolism  takes  place  in  these  tissues,  due,  pre- 
sumably, to  the  state  of  constant  slight  tension  or  ;;  tonus  "  of  the 
living  muscle. 

MINOR    MUSCULAK    MOTIONS. 

It  is  rarely  the  case,  however,  that  an  animal,  even  when  at  rest 
in  the  ordinary  sense,  does  not  execute  more  or  less  motions  of  various 
parts  of  the  body,  all  of  which  involve  an  expenditure  of  energy,  and 
even  apparently  insignificant  movements  may  materially  increase  the 
amount  of  metabolism. 

Zuntz  and  Hagemann,1  for  example,  report  a  respiration  experi- 
ment upon  a  horse  in  which  the  uneasiness  caused  by  the  presence  of 
a  few  flies  in  the  chamber  of  the  apparatus  caused  an  increase  of  10 
per  cent  in  the  metabolism.  Johansson 2  compared  the  excretion 
of  carbon  dioxid  by  a  fasting  man  when  simply  lying  in  bed  (awake) 
with  that  occurring  when  all  the  muscles  were  as  perfectly  relaxed 
as  possible.  The  results  per  hour  were : 

H.rcrction  of  CO,  by  fasting  man. 

Grams. 

Lyiii£  in  bed 24.04 

Complete   muscular   relaxation 20.72 

Benedict  and  Carpenter 3  have  compared  the  metabolism  of  men 
during  sleep  with  that  of  the  same  subjects  lying  quietly  in  bed  im- 
mediately after  waking.  In  the  three  cases  which  they  regard  as 
strictly  comparable  the  increase  in  the  heat  production  during  the 
waking  period  ranged  from  5.8  to  15.2  per  cent,  averaging  11.4 
per  cent. 

If,  then,  these  comparatively  insignificant  movements  have  such  a 
striking  effect  upon  the  metabolism,  it  is  evident  that  the  amount  of 
muscular  activity  must  be  an  important  factor  in  determining  the 

1  Landwirtschaftllche  Jahrbiichrr,  vol.  2.'?,  p.  ]<»!. 

-  Skanclinavischps  Arohiv  fiir  Physiologic,  vol.   8.  p.  S.">. 

8  Carnegie  Institution  of  Washington,  Publication  12«>.  p.  241. 

8489°— Bull.  143—12 5 


66  MAINTENANCE    RATIONS    OF   FARM    ANIMALS. 

relative  maintenance  requirements  of  two  animals  even  though  their 
minimum  physiological  requirements  may  be  identical.  In  experi- 
ments of  any  considerable  duration  on  normal  animals,  it  is  impossible 
to  avoid  more  or  less  expenditure  of  energy  in  this  incidental  muscular 
work,  while  it  is  often  a  matter  of  difficulty  to  make  the  different 
periods  of  an  experiment  comparable  in  this  respect. 


LYING    AND    STANDING. 


Furthermore,  considerable  muscular  exertion  is  involved  during  the 
waking  hours  in  maintaining  the  relative  position  of  the  different 
members  of  the  body.  This  is  notably  true  of  the  effort  of  standing. 
In  experiments  by  Armsby  and  Fries 1  the  heat  radiated  per 
minute  by  a  steer  while  standing  was  found  largely  to  exceed  that 
given  off  while  lying,  the  excess  in  25  experiments  ranging  from  28.3 
to  04.5  per  cent,  although  there  were  indications  that  the  amount  of 
feed  consumed  was  also  a  factor. 

On  the  other  hand  Dahm,'-  working  in  Zuntz's  laboratory  and  by 
his  methods,  found  an  increase  of  only  8  per  cent  in  the  respiratory 
excretion  of  C(X  by  a  young  bull  when  standing  as  compared  with 
that  when  h'ing.  but  Zuntz  3  himself  in  earlier  experiments  on  a  dog 
observed  differences  similar  to  those  found  by  Armsby  and  Fries  for 
cattle,  the  average  oxygen  consumption  per  minute  being  while  lying 
174.3  c.  c.  and  while  standing  24."). 0  c.  c.,  or  an  increase  of  41  per  cent. 
Benedict 4  observed  an  increase  of  from  13.3  to  18.8  per  cent,  or  an 
average  of  1C. 5  per  cent,  in  the  heat  production  of  man  when  standing 
as  compared  with  that  observed  when  sitting  quietly  in  a  chair. 

It  is  clear,  then,  that  of  two  animals,  one  of  which  lies  down  for  12 
hours  and  the  other  for  8  hours  out  of  the  24.  the  former  will,  other 
things  being  equal,  require  less  energy  for  maintenance.  In  the 
results  regarding  the  maintenance  ration  thus  far  reported,  with 
the  exception  of  the  Pennsylvania  experiments,  this  factor  has  not 
been  taken  into  account. 

INDIVIDUALITY. 

It  appears  quite  probable  that  those  differences  between  the  main- 
tenance requirements  of  different  animals  which  are  ascribed  some- 
what vaguely  to  i%  individuality  "  are  due  to  a  large  extent  to  varying 
amounts  of  muscular  activity.  In  general,  the  nervous,  restless 
animal  will  have  a  higher  maintenance  requirement  than  the  quiet, 
phlegmatic  one.  Thus  the  table  on  page  40  shows  that  Armsby  and 

1  Bureau  of  Animal    Industry.  Bulletins  ."I,  74.   101,  :ind  128. 

-  Biochemische  Zcitsclirift,  vol.  L'8.  p.  494. 

3  Arohiv  fiir  die-  gcsnmmto  Physiologic  des  Monschfn  und  dcr  Thiore  (Pfliigcr  i,  vol.  t;s, 
p.  191. 

*  Loc.   clt..    I>.   -M4. 


FACTORS   AFFECTING   THE   ENERGY   REQUIREMENT.  67 

Fries's  steer  A  had  in  every  case  a  materially  lower  maintenance 
requirement  than  steer  B,  even  when  the  results  were  corrected  to  an 
equal  number  of  hours  standing  per  day.  Computed  per  1.000  pounds 
live  weight  and  corrected  to  1_?  hours  standing,  the  results  for  avail- 
able energy  were  as  follows : 

Available  energy  required  far  ntaintennncr — Anmby  and  Fries. 


Steer  A. 

Steer  B. 

T/t<rm.i. 
1905                                  0.23 

Therms. 
7.06 

190C                         5.70 

0.38 

1907                                                                                                                                                            4  SO 

0  50 

Steer  B  was  an  animal  of  rather  pronounced  dairy  type  and  of  a 
nervous  disposition,  and  in  all  probability  his  higher  maintenance  re- 
quirement is  to  be  ascribed  to  this  fact.  There  can  be  little  doubt 
that  temperament  is  an  important  factor  in  determining  the  main- 
tenance requirement  and  that  there  may  be  a  considerable  range  of 
individual  differences  in  this  respect. 

Similarly,  any  conditions  tending  to  affect  the  degree  of  muscular 
activity  will  also  tend  to  affect  the  maintenance  requirement.  The 
steer  confined  in  a  stall,  for  example,  is  likely  to  take  less  muscular 
exercise  and  therefore  to  require  a  smaller  amount  for  maintenance 
than  one  simply  confined  to  a  pen  or  an  open  yard.  The  animal 
comfortably  bedded  and  thereby  induced  to  spend  much  of  his  time 
in  lying  down  will  consume  a  smaller  portion  of  his  feed  for  mainte- 
nance than  one  kept  under  less  comfortable  conditions.  Any  sort  of 
excitement  is  likely  to  cause  increased  muscular  activity  and  corre- 
spondingly increased  consumption  of  food  for  maintenance. 

CONDITION. 

The  condition  of  an  animal — that  is.  the  amount  of  adipose  tissue 
carried — seems  to  influence  the  maintenance  ration,  at  least  in 
the  case  of  cattle.  This  point  was  first  investigated  by  Kellner.1 
His  average  result  for  three  fat  cattle,  as  shown  in  the  table  on 
page  43.  is  considerably  higher  when  computed  to  the  same  live 
weight — that  is,  per  unit  of  surface — than  that  for  the  seven  lean 
animals,  viz : 

Unfattened 10.87  therms  metabolizable  pnerjry  per  1,000  pounds  live  weight. 

Fattened 15.05  therms  uietabolizable  energy  per  1,000  pounds  live  weight. 

Only  one  animal,  however,  was  common  to  the  two  groups,  A'iz, 
steer  B,  the  results  on  which  were  excluded  .from  the  average  of  the 
unfattened  animals  on  the  ground  that  it  was  abnormally  high,  since 
the  animal  never  lay  down  during  the  experiments.  Curiously 

1  Die  Lanchvirtschlichon  Versuchs-Stationen,  vol.  50,  p.  1M5  ;  vol.  .'>:'.,  p.  14. 


68  MAINTENANCE   RATIONS    OF    FARM   ANIMALS. 

enough,  this  animal  showed  the  lowest  maintenance  ration  of  the 
three  fattened  animals  and.  moreover,  one  which  is  distinctly  less 
per  unit  of  computed  surface  than  in  the  unf attened  state,  viz : 

Unfattened 14.  72  therms  metabolizable  energy  per  1,000  pounds  live  weight. 

Fattened 13.  80  therms  metabolizable  energy  per  1,000  pounds  live  weight. 

No  other  respiration  experiments  upon  the  relative  maintenance 
requirements  of  fattened  and  unfattened  animals  are  on  record. 
Evvard's  live-weight  results,  however,  as  given  in  the  table  on  page 
47,  appear  to  confirm  Kellner's  conclusion  that  the  relative  mainte- 
nance ration  of  fattened  animals  is  greater  than  that  of  the  same 
animals  unfattened. 

One  obvious  reason  why  the  maintenance  requirement  should  be 
greater  in  the  former  case  is  the  presumably  greater  muscular  effort 
expended  in  standing,  due  to  the  greater  weight  to  be  supported. 
Zuntz  and  Hagemann  in  experiments  upon  the  horse  carrying  weight 
on  its  back  found  that  this  increase  was  proportional  to  the  amount  of 
weight  added.  The  increase  indicated  by  Kellner's  averages,  how- 
ever, is  greater  than  would  be  computed  on  this  assumption,  and  the 
same  is  true  of  Evvard's  fat  animals,  the  difference  becoming  greater 
as  the  animals  become  fatter. 

AGE. 

The  energy  requirement  of  a  young  animal  is  naturally  smaller  per 
head  than  that  of  an  older  animal  on  account  of  the  difference  in 
size.  Whether  there  is  any  difference  in  the  relative  requirements — 
that  is,  in  the  requirement  computed  to  uniform  weight  or  surface — 
is  not  altogether  clear,  few  specific  results  on  farm  animals  being  on 
record.  Evvard's  results  on  yearlings,  page  40,  are  somewhat  higher 
than  most  of  the  results  which  have  been  obtained  with  mature 
cattle,  although,  of  course,  these  figures  do  not  refer  to  the  same 
individuals  at  different  ages.  Armsby  and  Fries,1  in  a  series  of  respi- 
ration calorimeter  experiments  upon  the  same  two  animals  in  three 
successive  years,  observed  a  progressive  decrease  in  the  maintenance 
requirement  of  yearlings,  2-year-olds,  and  3-year-olds  when  corrected 
to  a  uniform  number  of  hours  standing  and  computed  to  equal  ex- 
ternal surface  (that  is,  in  proportion  to  the  two-thirds  power  of  the 
weight ) . 

Somewhat  extensive  data  are  on  record  regarding  the  metabolism 
of  man  at  different  ages.  A  summary  and  discussion  of  these  by 
Tigerstedt  -  seem  to  show  clearly  that,  leaving  out  of  account  infants 
and  very  aged  persons,  the  metabolism  per  unit  of  surface  diminishes 
from  youth  to  maturity.  Tn  view  of  the  slow  development  of  man. 
these  results  are  comparable  to  such  as  might  be  obtained  during  the 
first  0  to  12  months  of  the  life  of  ordinary  domestic  animals  and  for 

1  I*in-i';iu  of  Animal   Industry,  Ilullctin   12S,  p.  n."i. 

"  Xatfol's  Ilnnclbuch  dcr  Pliysiologip  dcs  Mcnschon,    I,  469. 


EXTERNAL   TEMPERATURE.  69 

these  ages  we  have  few  satisfactory  determinations  of  the  mainte- 
nance requirement.  The  results  upon  swine  cited  on  previous  pages 
seem,  it  is  true,  to  indicate  the  contrary  relation,  viz,  a  lower  relative 
maintenance  requirement  for  young  animals.  These  results,  how- 
ever, are  based  upon  live-weight  experiments  and,  as  already  noted, 
are  possibly  lower  than  the  true  maintenance  ration. 

If  it  be  true  that  the  maintenance  rations  of  young  animals  are 
relatively  greater  than  those  of  older  ones,  we  may  fairly  presume  it 
to  be  due  to  a  considerable  extent  to  the  greater  amount  of  muscular 
activity  usually  exhibited  by  young  animals. 

EXTERNAL,   TKM  PKRATIHK. 

Farm  animals  belong  to  that  general  class  known  a.s  warm-blooded 
or  homoiothermic  animals,  whose  bodies  maintain  a  nearly  constant 
temperature  during  health,  regardless  of  that  of  their  surroundings 
unless  the  latter  be  extreme,  in  which  case  death  soon  results. 

REGULATION    Ol'    BODY    TKMI'KRATVKK. 

Obviously,  the  regulating  mechanism  which  maintains  a  constant 
temperature  in  spite  of  variations  in  the  heat  production  of  the  body 
and  in  the  temperature  of  its  surroundings  must  be  very  efficient 
and  very  exactly  adjusted.  The  regulation  is  effected  in  general  in 
tVo  ways,  which  may  be  called,  respectively,  physical  and  chemical 
regulation. 

The  heat  of  an  animal  escapes  from  the  surface  of  tne  bod}'  chiefly 
through  the  skin,  but  to  some  extent  also  through  the  air  passages, 
being  removed  both  by  conduction,  by  radiation,  and  by  the  evapora- 
tion of  water.  A  rise  of  external  temperature  tends  to  check  the  out- 
flow of  heat  exactly  as  it  would  in  the  case  of  an  inanimate  body. 
This  tendency  is  compensated  by  a  nervous  reflex,  which  allows  the 
capillary  blood  vessels  of  the  skin  to  enlarge  so  that  more  blood  flows 
through  them,  thus  tending  to  raise  the  temperature  of  the  surface 
and  increase  the  outflow  of  heat.  This  phenomenon  is  readily  ob- 
served in  the  flush  which  follows  exposure  to  high  temperatures.  This 
method  of  regulation  is  analogous  to  opening  the  windows  of  a  room 
to  cool  it.  If  the  external  temperature  continues  to  rise,  perspiration 
appeal's,  or  in  the  case  of  animals  that  have  no  sweat  glands,  like  the 
dog.  a  peculiar  form  of  breathing  sets  in.  and  relatively  large  amounts 
of  water  are  evaporated  from  the  skin  or  from  the  tongue  and  the  in- 
terior of  the  mouth  and  throat.  In  this  way  large  quantities  of  heat 
are  carried  off  as  the  latent  heat  of  evaporation  <>f  water,  somewhat  as 
an  overheated  room  may  be  cooled  by  sprinkling  the  floor.  When  the 
external  temperature  falls  again,  the  process  is  reversed.  Sensible 
perspiration  decreases  and  the  blood  is  diverted  from  the  capillaries 
of  the  skin  to  the  internal  capillaries.  If  this  happens  too  quickly,  it 


70 


MAINTENANCE   RATIONS    OF    FARM   ANIMALS. 


may  even  lead  to  congestion  of  the  latter.  The  process  is  analogous 
to  the  closing  of  the  windows  of  a  room  as  the  weather  grows  colder. 
There  is  evidently  a  limit  to  this  method  of  regulation.  If  the 
windows  are  entirely  closed  nothing  more  can  be  effected  in  this 
manner,  and  if  the  weather  continues  to  grow  colder  the  fire  in  the 
room  must  be  increased.  So  if  the  external  demand  for  heat  becomes 
so  great  as  to  exceed  the  limits  of  adjustment  in  the  body  more  fuel 
material  is  katabolized — that  is,  more  heat  is  produced.  This  was 
first  demonstrated  by  Carl  Voit,  who  obtained  the  following  results 
for  the  excretion  of  carbon  dioxid  by  a  man  at  various  temperatures: 

Influence  <jf  external  temperature  on  -metabolism  of  man — Carl  Voit. 


Tempera- 
ture. 

Carbon         Urinary 
dioxid.     ;    nitrogen. 

Tempera- 
ture. 

Carbon 
dioxid. 

Urinary 
nitrogen. 

'C. 

4.4 
0.5 
9.0 
14.3 

Grams.          Grams. 
210.  7                4.  23 
206.  0                4.  05 
192.0    '            4.20 
155.  1     !            3.  SI 

;      °e. 

23.7 

24.2 
26.7 
30.0 

Grams. 
164.8 
166.5 
160.0 
170.6 

Gramg. 
3.40 
3.34 
3.97 

16.2 

158.3     -            4.00 

Later  and  more  comprehensive  experiments  with  animals  by  Rubner  have 
given  corresponding  results.  Thus  with  two  guinea  pigs  the  following  figures 
were  obtained  in  24-hour  experiments:1 


Influence  of  e.rternal  temperature  on  metabolism 

Mature  animal.  Young  animal. 


TptnnpM    I  Tempera-       Copper    j  TemDer,       Tempera- 
ture of         kilogram    !  ture  of 
tureofair.      animal-       anil^onr.     f'»«of*'r-      animal. 


CQ2  per 
kilogram 
and  hour. 


'C. 

0 

11.1 

20.8 
25.7 
30. 3 
.34.  9 
40.0 


Grams. 
2. 905 
2.  151 
1.7f)6 
1.5)0 
1.317 
1 . 273 
1 . 454 


Grams. 
4. 500 
3. 4.33 
2. 2X3 

1.778 
2.  260 


A  later  experiment  by  Rubner  '  upon  a  dog.  in  which  the  heat  production  was 
measured  by  a  calorimeter,  gave  the  following  results; 


Hoat  pro- 

Tempera-        duct  ion 
lure  (if  :iir.  per 

kilogram. 


ClosHzo,  p.   1  '•>. 


-Aivliiv  fiir  Ily-irnc.   vol.   11,  p.  2R5. 


FEED   CONSUMPTION    A   SOURCE   OF    HEAT.  71 


CRITICAL    TKMPKBATVRK. 


Tt  is  clear  from  the  foregoing  results  that  when  the  external  tem- 
perature falls  below  a  certain  limit  the  heat  production  of  the  animal 
shows  a  marked  increase.  This  point  at  which  the  physical  regula- 
tion gives  way  to  or  begins  to  be  supplemented  by  the  chemical  regu- 
lation has  been  called  the  "critical  temperature"'  for  the  animal. 
Above  this  temperature  the  radiating  capacity  of  the  body  surface 
is  varied  to  meet  the  varying  conditions:  below  it  this  method  of 
regulation  is  largely  exhausted,  and  therefore  the  heat  production 
is  varied  to  suit  the  needs.  This  latter  so-called  chemical  regulation 
is  probably  effected  largely  in  the  muscles,  either  by  visible  motion 
or  by  increase  in  the  muscular  tonus.  either  of  which  involves  an 
increased  heat  production.  This  has  been  clearly  shown  to  be  true 
of  man  and  probably  applies  also  to  other  animals.  Above  the 
critical  temperature  there  appears  to  be  a  slight  increase  in  the  heat 
production  with  rising  temperature,  probably  due  to  the  additional 
energy  required  for  the  various  processes  of  physical  regulation. 

Any  conditions  tending  to  facilitate  the  escape  of  heal  from  the 
body  would  obviously  act  like  a  fall  of  temperature.  Wind,  for  ex- 
ample, by  removing  the  layer  of  partially  warmed  air  next  to  the 
skin,  tends  to  remove  the  heat  more  rapidly  from  the  body,  so  that 
(he  cold  is  felt  more  severely  on  a  windy  day.  while,  on  the  other 
hand,  the  effect  of  a  high  temperature  is  modified  by  wind.  A  high 
percentage  humidity  of  the  air  on  a  warm  day  hinders  the  removal  of 
heat  by  evaporation,  so  that  a  moist  heat  is  more  trying  than  a  dry 
heat.  Cold,  moist  air.  on  the  other  hand,  facilitates  the  escape  of  heat 
from  the  body  by  increasing  the  conducting  power  of  the  clothing, 
hair,  or  fur.  so  that  a  damp  cold  is  more  severe  than  a  dry  cold.  The 
direct  rays  of  the  sun  may  impart  a  considerable  amount  of  heat  to 
the  body,  thus  moderating  the  effect  of  low  temperature  and.  on  the 
other  hand,  increasing  that  of  high  temperature. 


FI:I-:II  roxsrMPTioN   A   soriK'i:  OF  HEAT. 


For  the  sake  of  simplicity,  the  foregoing  paragraphs  have  dealt 
especially  with  the  case  of  the  fasting  animal,  neglecting  one  im- 
portant source  of  heat.  viz.  the  consumption  of  feed.  As  was  shown 
on  pages  10-2S.  the  latter  results  in  increasing  the  katabolism  of  the 
body,  and  whether  this  be  considered  the  result  of  (he  work  of  digestion 
or  simply  designated  as  specific  dynamic  effect,  the  fact  is  established 
beyond  question.  This  heat,  however,  once  generated,  while  unavail- 
able for  the  physiological  processes  of  the  body  is  ju><  a<  useful  as  ex- 
ternal heat  for  keeping  it  warm.  Tn  other  words,  the  consumption  of 
feed  will  tend  to  have  the  same  effect  as  a  rise  of  external  tempera- 


72  MAINTENANCE   RATIONS    OF    FARM    ANIMALS. 

ture.  This  being  the  case,  it  is  clear  that  at  temperatures  consider- 
ably below  the  critical  temperature,  all  the  metabolizable  energy  of  the 
feed  will  be  of  use  to  the  body.  Part  of  it  will  be  available  for 
physiological  uses  as  already  explained,  but  the  remainder,  while  not 
available  in  this  sense  will  nevertheless  be  of  use  as  a  source  of  heat. 

ISODYNAMIC    REPLACEMENT. 

It  was  upon  his  earlier  experiments  (published  in  1883)  made  un- 
der substantially  the  conditions  just  indicated  that  Rubner  based 
his  famous  law  of  isodynamic  replacement  of  nutrients  which  has 
played  a  large  part  in  the  discussion  of  nutrition  problems.  This 
law  may  be  briefly  stated  as  follows:  In  amounts  less  than  a  main- 
tenance ration  the  nutrients  replace  each  other  or  ~body  tissue  in  in- 
rerse  proportion  to  their  metabolizable  energy.  The  quantities  which 
thus  replace  each  other  are  accordingly  said  to  be  isodynamic.  Tt 
need  scarcely  be  pointed  out  that  the  minimum  of  protein  required 
for  the  maintenance  of  the  nitrogenous  tissues  is  not  included  under 
this  law.  Rubner  was  careful  to  limit  the  law  to  small  amounts  of 
food.  Tn  his  earlier  publications  he  stated  that  it  holds  only  below 
the  maintenance  ration:  somewhat  later  he  asserted1  that  it  obtains 
up  to  an  excess  of  about  50  per  cent  over  the  maintenance  requirement. 

These  results  of  Rubners  have  passed  into  the  literature  of  physi- 
ology and  are  still  largely  interpreted  as  representing  the  relative 
values  of  nutrients,  while  Rubner's  factors  for  the  metabolizable 
energy  of  nutrients  have  been  extensively  used  in  computing  the 
energy  values  not  only  of  human  dietaries  but  of  stock  rations  as 
well.  Historically.  Rubner's  earlier  investigations  mark  an  epoch 
in  the  science  of  nutrition.  While  similar  views  had  previously 
been  advanced  by  others.  Rubner  appears  to  have  been  the  first  to 
investigate  the  subject  experimentally.  The  conception  that  the 
replacement  values  of  the  nutrients  could  be  measured  by  the  rela- 
tive contributions  of  energy  which  they  in  alee  to  the  activities  of 
the  body  was  a  contribution  of  the  first  order  to  the  study  of  nutri- 
tion problems,  but  the  exact  form  given  it  in  these  earlier  experi- 
ments proves  to  have  been  but  a  partial  expression  of  the  truth,  as 
Rubner's  own  later  experiment,  as  well  as  tho-e  of  others,  have  fully 
demonstrated.  (Compare  pp.  20-28.) 

RELATION     01       M  A  I  NTKN A NCK     RATION     TO     CRITICAL     TKM  PKRATfRK. 

When  its  surroundings  are  above  the  critical  temperature,  the 
animal  is  producing  a  surplus  of  heat  as  a  consequence  of  its  neces- 
sary physiological  activities  and  disposes  of  it  by  the  processes  of 


CRITICAL   TEMPERATURE.  73 

physical  regulation  already  described.  The  heat  produced  is  then  in 
a  sense  an  excretum,  and  under  these  conditions  obviously  the  ex- 
ternal temperature  does  not  materially  affect  the  maintenance  ration. 
The  latter,  as  already  shown,  is  measured  by  the  amount  of  available 
energy  necessary  to  support  the  vital  processes,  i.  e.,  by  the  total 
fasting  katabolism. 

Below  the  critical  temperature,  however,  the  conditions  are  differ- 
ent. At  relatively  low  temperatures  all  the  metabolizable  energy  of 
the  feed  is  used  directly  or  indirectly  to  keep  the  animal  warm,  and 
as  the  external  temperature  falls,  either  more  feed  must  be  given  or 
more  tissue  burned  to  supply  the  additional  heat  required  to  main- 
tain the  body  temperature. 

FEED    CONSUMPTION    LOWERS    THE    CRITICAL    TEMPERATURE. 

Since  feed  consumption  is  itself  a  source  of  heat,  the  animal  con- 
suming feed  can,  other  things  being  equal,  withstand  a  lower  tem- 
perature than  when  fasting,  and  the  larger  the  amount  of  feed 
consumed  the  lower  is  the  corresponding  temperature.  The  matter 
may  also  be  put  in  the  reverse  way.  For  any  particular  (low)  tem- 
perature there  is  a  certain  amount  of  feed  the  digestion  and  assimila- 
tion of  which  will  yield  an  amount  of  heat  sufficient  to  supplement 
that  derived  from  the  fasting  katabolism,  so  as  to  just  maintain  the 
body  temperature.  This  particular  external  temperature,  then,  is 
the  critical  temperature  for  that  amount  and  kind  of  feed,  and,  con- 
versely, that  particular  ration  may  be  called  the  critical  amount  of 
feed  for  the  particular  external  temperature. 

CRITICAL   TEMPERATURE   FOR    FARM    ANIMALS. 

The  critical  temperature  for  farm  animals  has  not  been  definitely 
determined.  In  the  case  of  cattle  and  probably  of  sheep,  however,  it 
is  apparently  rather  low  for  animals  consuming  an  ordinary  ration. 
Thus  Armsby  and  Fries  have  found  that  at  about  18°  C.  the  ration 
of  cattle  can  be  reduced  considerably  below  the  maintenance  require- 
ment without  any  evidence  of  increased  oxidation  of  tissue  for  the 
sake  of  heat  production.  In  the  case  of  fattening  animals  consuming- 
heavy  rations  and  therefore  producing  a  large  amount  of  heat  as  a 
result  of  digestive  work,  the  criticsil  temperature  would  be  still  lower 
and  experiments  upon  such  animals  have  shown  that  they  may  be 
exposed  to  comparatively  low  temperatures,  as  in  an  open  shed  or 
yard,  without  causing  them  to  oxidize  any  more  food  material.  As 
already  stated  (p.  50)  the  critical  temperature  for  the  horse  appears 
to  be  relativelv  higher. 


74  MAINTENANCE   RATIONS   OF   FARM   ANIMALS. 

THE  PROTEIN  REQUIREMENT  FOR  MAINTENANCE. 
PROTEIN"   KATABOLIZED  DURING  FASTING.1 

It  has  already  been  shown  on  pages  11-12  that  in  the  previously 
•well-nourished  fasting  animal  the  katabolism  of  protein  supplies 
but  a  small  part  of  the  total  energy  required  for  the  support  of  the 
vital  functions.  As  a  preliminary  to  the  consideration  of  the  protein 
requirement,  however,  some  further  consideration  of  the  protein 
katabolism  during  fasting  is  desirable. 

INFLUENCE    OF    PREVIOUS    FEED. 

The  classic  experiments  of  Carl  Voit  upon  fasting  dogs  showed 
that  while  the  protein  katabolism  in  the  early  days  of  fasting  may 
vary  widely 'according  to  the  previous  feed,  it  soon  falls  to  a  com- 
paratively low  level  which  is  approximately  the  same  for  the  indi- 
vidual animal  whatever  its  amount  upon  the  initial  days.  This 
behavior  is  well  illustrated  by  the  following  results,  all  upon  the 
same  animal,  which  have  been  fully  confirmed  by  numerous  subse- 
quent experiments.2 

Protein  kutfiboUxm  of  fa  si  ing  dog — Voit. 


2,500  grams 
meat. 


grams  fat. 


Bread. 


Urinary  nitrogen  *  per  day: 
Last  dav  of  feeding  

Gram.'! 
84 

4 

G  ra  m$. 
00 

Grams. 
51 

Grams 
51 

Grams. 
11.5 

28 

1 

17 

:; 

13 

q 

12 

4 

9.1 

Second  dav  of  fasting 

11 

6 

10 

<» 

8 

8 

7.3 

8 

q 

8 

8 

2 

3 

7.0 

Fourth  dav  of  fasting 

.   .                  8 

1 

6 

9 

0 

n 

6.2 

Fifth  day  of  fasting 

5 

P 

6 

6 

6 

« 

5.9 

G 

•i 

6 

0 

6. 

1 

6 

n 

6.1 

Seventh  dav  of  fasting 

s 

0 

fi 

6 

n 

Eighth  dav  of  fasting  

4 

6 

0 

6 

\ihth  dav  of  fasting 

fi 

Tenth  dav  of  fasting.  .  . 

r> 

3 

I  ASTINC    KATA1JOI.ISM    VAKI AI5I.K. 


It  is  not  true,  however,  as  is  sometimes  loosely  stated,  that  the 
protein  katabolism  of  a  fasting  animal  is  a  constant  quantity.  On 
the  contrary,  in  the  presence  of  an  adequate  amount  of  body  fat.  its 
amount  tends  to  diminish  with  t]ie  progress  of  fasting.  This  fact 
appears  more  or  less  clearly  in  the  foregoing  experiments,  while  in 
later  ones  it  is  quite  marked.  For  example,  in  the  experiments  by 


1  Compare   references  on   \>.   s. 

-  Zcitschrift    fur  r.iolo^ie.   vol.   L'.   p.  :!07. 

:l  Computed  from  Voit's  fijrures  for  urea.  In  earlier  experiments  upon  the  protein 
metabolism  the  urea  in  the  urine,  as  determined  by  I.iebiji's  titration  method,  was  com- 
monly taken  as  the  measure  of  protein  katabolism.  I.aler  experience  has  shown  that 
these  results  are  r,<>t  strietly  accurate,  but  the  amount  of  urea  under  such  circumstances 
is  so  nearly  proportional  to  the  total  urinary  nitrogen  thai  the  results  as  given  above  are 
entirely  adequate  as  an  illustration  of  the  point  under  discussion. 


THE    MINIMUM    OF    PROTEIN. 


75 


Benedict,  cited  on  page  15  in  illustration  of  the  relative  constancy  of 
the  energy  katabolism,  the  total  protein  katabolism  showed  a  distinct 
falling  off,  and  the  same  is  true  in  less  degree  when  computed  per 
kilogram  weight.  The  total  urinary  nitrogen  upon  the  several  davs 
of  the  experiment  was: 


J'i'otcin    Icntubolixtn-  <>f  faxting   ninn  —  I 


Days. 

Urinary 
Total. 

nitrogen. 

Urinary  nitrogen. 

Per  kilo- 
gram 
weight. 

Per  kilo- 
Total,         gram 
weight. 

1    

Grams. 
12.24 
12.45 

Gram. 
0.  20C      5 

Grams.        Gram. 
10.  S7            0.191 
10.74              .190 
10.  13              .  181 

2 

.211      0 

3                       

13.02 

4  

11.63 

.202  ' 

E.  and  O.  Freuud *  determined  the  daily  nitrogen  excretion  of  Succi.  a  pro- 
fessional faster,  with  the  following  results: 

Protein  kntaboliam  of  fasting  »wn — E.  ami  O.  Freund. 


Days. 


Nitrogen. 


Days. 


Nitrogen. 


Nitrogen. 


Grams. 
17.0 

8 

Grams. 
9.74 

15 

Gr'im.t 

11.2 

9  

10.  05 

1*; 

.j 

10.  55 

7.12 

Ofi 


5 !         11.19      12.... 

6 1         11.01       13.... 

7 8.79      14. 


fi.S4    '19 

5.14      20 

4.  ..10    ,  21... 


A  similar  phenomenon  was  observed  by  Mkhaud  in  rxiieriments  on  the  rela- 
tive value  of  proteins  described  on  a  subsequent  page.  A  dog.  after  44  days  ab- 
stinence from  protein  (1C  days  without  food  followed  by  2*  on  nounitrogenous 
food),  excreted  daily  1.42  grams  nitrogen.  The  same  dog  after  prolonged  feeding 
upon  low  protein  rations,  however,  showed  in  a  three-days  fast  an  average  daily 
excretion  of  only  0.95  grains  nitrogen.  On  the  other  hand,  however,  as  already 
pointed  out.  the  fasting  protein  katabolism  may  show  a  very  marked  increase 
with  the  progress  of  fasting  in  the  absence  of  a  sntiicienr  store  of  body  fat. 
It  appears,  then,  that  in  fasting  the  protein  katabolism  is  much  more  variable 
in  amount  than  the  total  kntabolism,  and  this  fact  must  be  remembered  in  any 
discussion  of  the  protein  requirement. 

TIIK    MINIMUM    OK    PROTEIN. - 

It  is  evident  that  the  comparatively  small  amount  of  protein  kata- 
bolized  in  the  fasting  animal  so  long  as  its  store  of  fat  is  reasonably 
abundant  is  at  least  all  that  is  absolutely  essential  to  the  vital 

1  Cited  by   Lusk. 

2  For  a  moro  exhaustive  discussion  of  the  subjects  of   this   ami  succeeding  paragraphs, 
including   references   to   the   literature,    compare    the-    rrtVi-.>n<vs   on    pa  ire    S.    in    particular 
Magnus-Levy,  pp.   108-423;  Tigerstedt,  pp.  .''.0 1-4 SO  ;  Lusk.  Chapters  TV  and  V. 


76  MAINTENANCE   BATIONS    OF   FARM   ANIMALS. 

processes,  since  the  latter  go  on  for  a  considerable  time  in  a  sub- 
stantially normal  manner.  The  question  at  once  arises  whether  this 
fasting  katabolism  represents  the  amount  of  digestible  protein  -which 
must  be  supplied  in  the  feed  in  order  to  maintain  the  protein  tissues 
of  the  body. 

1NFLUKXCF.     OF     NOXN1TROGKXOUS     MATFRIAI.S. 

In  the  first  place,  it  is  to  be  remarked  that,  as  just  shown,  the 
protein  katabolism  during  fasting  is  by  no  means  a  fixed  and  definite 
quantity,  but  may  vary  even  in  the  same  individual  within  quite 
wide  limits  both  absolutely  and  as  regards  the  proportion  of  the 
total  energy  requirement  which  is  supplied  by  it.  From  the  results 
cited  on  pages  12-13,  it  is  evident  that  a  most  important  factor 
influencing  the  fasting  katabolism  is  the  stock  of  fat  in  the  body 
and  that  when  the  latter  is  reduced  protein  is  katabolized  for  the 
sake  of  its  energy.  In  other  words,  a  lack  of  readily  available  non- 
nitrogenous  material  in  the  body  tends  to  increase  the  protein 
katabolism  above  its  minimum  value.  Evidently,  then,  in  seeking 
to  determine  the  minimum  amount  of  protein  required  for  main- 
tenance, the  food  given  should  contain  a  liberal  supply  of  non- 
nitrogenous  nutrients  to  supply  the  necessary  energy  for  the  animal, 
since  otherwise  there  is  danger  that  the  protein  will  be  katabolized 
for  this  purpose,  resulting  in  an  apparent  increase  of  the  maintenance 
requirement. 

KEI.ATIO>:    TO    FASTING    KATABOLISM. 

In  the  early  experiments  upon  this  subject,  especially  those  of  Voit,  the  full 
significance  of  this  fact  had  not  been  recognized.  His  experiments,  in  which 
increasing  amounts  of  protein  alone  were  fed  (compare  p.  7!)').  showed  that 
protein  equal  to  two  and  a  half  to  three  times  the  fasting  katabolism  was 
necessary  to  reach  nitrogen  equilibrium,  and  this  result  was  generalized  and 
passed  current  for  a  considerable  time. 

Munk  1  seems  to  have  been  the  first  to  challenge  this  view  and  to  claim  not 
only  that  an  amount  of  protein  equal  to  that  katabolized  during  fasting  is 
adequate,  but  that  with  an  abundant  supply  of  nonnitrogenous  material,  "spe- 
cially carbohydrates,  in  the  feed  a  notably  smaller  amount  of  protein  is  suffi- 
cient lo  maintain  the  nitrogen  balance.  Munk's  experiments  either  include  no 
comparison  with  the  fasting  katabolism  of  the  same  animal  or  a  comparison 
not  in  all  res[>ects  satisfactory,  but  they  show  clearly  that  nitrogen  equilibrium 
was  maintained  on  a  supply  of  protein  less  than  that  usually  found  to  be 
katabolized  in  similar  fasting  animals. 

On  the  other  hand,  extensive  experiments  by  Voit  and  Korktinoff*  on  dogs 
led  these  experimenters  to  an  opposite  conclusion.  Starting  with  a  ration 
deficient  in  protein  but  containing  a  very  liberal  supply  of  nonnitrogenous 
nutrients,  the  protein  of  the  feed  was  gradually  increased  until  an  amount  was 

'Virchow's  Arcliiv  fur  Patliolo-rische  Anatomic  und  Pliysiologie  mid  fur  Klinisclu-  Medi- 
um, vol.  101,  p.  01  ;  vol.  1. ':."..  Supp.  ;  vol.  l.'iL',  p.  5)1.  Archiv  filr  (Anatomie  und  i  Physi- 
olonie.  1*5)0.  p.  IS.'!. 

-  Xfitschrift   fiir   Biologie,   vol.   :\'2,   p.   58 


THE    MINIMUM    OF    PROTEIN. 


77 


reached  sufficient  to  produce  equilibrium  between  the  income  and  outgo  of 
nitrogen.  Two  series  of  experiments  were  performed,  in  one  of  which  the  non- 
nitrogenous  nutrients  consisted  chiefly  of  f;it,  and  another  in  which  they  con- 
sisted of  carbohydrates.  Considering  only  those  experiments  in  which  the  feed 
consumed  was  more  than  sufficient  in  amount  lo  supply  the  estimated  demand 
of  the  body  for  energy,  it  was  found  that  when  the  nonnitrogeuous  nutrients 
consisted  of  fat  the  nitrogen  (protein)  of  the  feed  had  to  be  increased  to  ap- 
proximately 130  per  cent  of  the  amount  kataboli/.ed  in  fasting  before  nitrogen 
equilibrium  was  reached — that  is,  before  the  stock  of  body  protein  was  main- 
tained. When,  however,  the  energy  demands  of  the  body  were  supplied  by 
carbohydrates  instead  of  fats,  a  supply  of  nitrogen  (protein)  in  the  feed  equal 
to  or  even  somewhat  less  than  the  amount  katabolized  in  fasting  snfliced  to 
insure  nitrogen  equilibrium.1  Cremer  and  Henderson,2  in  experiments  on  a 
dog  with  a  ration  estimated  to  supply  the  necessary  energy  for  maintenance, 
were  unable  to  maintain  nitrogen  equilibrium  on  even  as  small  an  amount  as 
did  Voit  and  Korknnoff. 

In  the  case  of  man,  on  the  other  hand,  numerous  experiments  seem  to  have 
demonstrated  that  an  amount  of  feed  protein  notably  less  than  the  ordinary 
fasting  katabolisui  is  sufficient  to  maintain  nitrogen  equilibrium,  although 
even  in  this  case  the  comparison  in  nearly  every  case  is  with  the  average 
fasting  katabolism  and  not  with  that  of  the  individual  under  experiment. 
This  average  for  man,  however,  has  been  well  established  by  numerous  experi- 
ments and  seems  not  to  vary  widely  for  individuals,  while  in  Benedict's  ex- 
periments3 upon  nutrition  after  fasting  a  material  diminution  of  the  protein 
katabolism  of  the  subject  was  observed  on  the  second  and  third  days.  In  every 
case  the  body  lost  protein,  but  in  experiments  70  and  74  there  was  a  storing  up 
of  energy. 

Protein  l;uinJ>oUxtn  during  <tnd  after  fasti-nr/.4 


Experi- 
ments (19 
and  70. 

Experi- 
ments 71 
and  72. 

E  xperi- 
ments  73 
and  74. 

Experi- 
ments 7.1 
and  70. 

Fasting:                  ,                                                                     Grams. 
First  dav.  00.  5 

Grama. 

35  o 

Gramx. 

til  7 

Grams. 
73  4 

Second  dav  ...                                                              '           85.  0 

li<i  2 

71  S 

74  7 

Third  dav".  90.  2 

7.S  0 

do  ••> 

7S  1 

Fourth  dav  .                                                                               77  S 

04  4 

(;•>  3 

04  8 

Fifth  dav  

50  (t 

05  2 

Sixth  dav  

64  4 

Seventh  dav  

60  8 

Food  after  fasting: 
First  dav                                                                         !           7S  ->4 

i!3  00 

i>4  44 

61  0° 

Second  dav                                                                                 50.  04 

40  50 

40  go 

Third  dav                            .   .                           ...                   (iO.  00 

40  tiS 

46  92 

Another  factor  which  must  be  taken  into  consideration  in  fixing  the  minimum 
of  protein  is  what  may  be  called  the  time  element.  liubner  calls  attention 
to  the  fact  that  if  the  protein  of  the  ration  is  consumed  at  a  single  meal  then1 
may  be  for  a  time  a  surplus  of  protein  or  its  digestive  products  in  the  system. 

1  Voit  and  Korknnoff  put  a  different  interpretation  upon  their  results,  basing  it  upon 
the  fact  that  a  certain  portion  of  the  urinary  nitrogen  is  derived  from  the  nitrogenous 
extractives  of  the  flesh  metabolized  in  the  body.  Compare  the  account  of  their  experi- 
ments in  the  writer's  Principles  of  Animal  Nutrition,  pp.  K'.fi-lMO. 

•  Zeitschrift  fiir  Biologie.   vol.  41'.  p.   G12. 
3  Loc.  cit.,  pp.  4r>0  and   r>'2^. 

*  The  odd-numbered  experiments  were  the  fasting  experiments.      The  even-numbered  ar.» 
those  in  which  food  was  given  and  which  immediately  followed  the  corresponding  fasting 
experiments. 


78  MAINTENANCE    RATIONS    OF    FARM    ANIMALS. 

while  at  a  subsequent  period  of  the  day  there  may  be  a  deficiency  which  will 
be  made  good  by  a  draft  upon  the  proteins  of  the  tissues. 

For  the  pin-pose  of  this  discussion,  it  is  unnecessary  to  pursue 
further  the  somewhat  complicated  question  of  the  absolute  pro- 
tein minimum  and  its  relations  to  the  fasting  protein  katabolism, 
especially  in  view  of  the  fact  that,  as  has  been  shown,  the  latter  is 
itself  more  or  less  variable.  It  appears  well  established  that  on  a  diet 
containing  an  abundance  of  carbohydrates  a  supply  of  protein 
equivalent  to  the  fasting  protein  katabolism  is  sufficient  to  meet  the 
needs  of  the  organism,  while  it  is  possible  that  a  less  amount  will 
suffice.  Fats  appear  to  be  distinctly  less  efficient  than  carbohydrates 
in  keeping  the  protein  katabolism  at  the  minimum.  Precisely  why 
this  is  the  case  has  not  been  fully  made  out,  although  Landenrren  l 

v  ~  O 

has  advanced  the  explanation  that  a  minimum  of  carbohydrates  is 
essential  to  the  chemical  processes  of  metabolism  and  that  when  a 
sufficient  amount  is  not  supplied  in  the  feed,  protein  is  katabolized 
for  the  sake  of  producing  carbohydrates,  with  the  result  that  on  a 
low  protein  diet  nitrogen  katabolism  is  increased.  In  any  case,  it 
is  clear  that  the  protein  requirement  upon  a  mixed  ration  sufficient 
in  quantity  is  comparatively  small. 

EFFECT    OF    SriU'I.rS    OF    PROTEIN. 
I.NCKKASKS    PKOTKIX    KATABOLISM. 

But  while  a  relatively  small  quantity  of  digestible  protein  is  suffi- 
cient, in  the  presence  of  an  abundant  supply  of  fuel  material,  to  main- 
tain the  body  in  nitrogen  equilibrium,  an  increase  of  the  feed  protein 
above  this  minimum  does  not  result  in  any  large  or  long-continued 
gain  of  protein  tissue  by  the  mature  animal,  but  causes  a  correspond- 
ing increase  in  the  protein  katabolism,  as  is  shown  by  the  prompt 
increase  in  the  amount  of  nitrogen  excreted  in  the  urine. 

This  fact  was  demonstrated  more  than  50  years  ago  by  C.  Voit.  in  collabora- 
tion at  first  with  Bischoff2  and  later  alone  and  with  Pettenkofer,3  in  experiments 
on  carnivorous  animals,  and  almost  innumerable  subsequent  investigations  have 
shown  that  it  is  true  not  only  of  these  animals,  but  of  man  and  of  herbivorous 
animals  as  well.  The  protein  katabolism  is  determined  chiefly  by  the  supply 
of  digestible  protein  in  the  feed,  and  the  body  comes  quite  promptly 
into  equilibrium  with  any  amount  above  the  maintenance  requirement  which 
can  be  consumed,  the  nitrogen  of  the  excreta  substantially  equaling  that  of  the 
1'eed.  This  is  well  illustrated  by  the  following  selection  from  Bischoff  and 
Voit's  results  upon  a  'log.4  arranged  in  the  order  of  the  amount  of  protein 
eaten. 

'•  Jiihresbrricht  fiber  die  Korhi-liriile  <lcr  TiiT-Chemie,  vol.  32.  p.  G85. 

-Geset/.e   dor   Ernithrung  des    Fleisclifrc.s^ers,   1860. 

"Published  chiefly  in  the  Annalen  dcr  Chcmie  und  Pharmacie  and  the  Zeitschrift  fiir 
Kioloi?ie.  See  also  Voit  :  "  Pbysiologie  des  Stoffwechsels,"  in  Hermann's  Handbucb  der 
Physiologie. 

1  Voit's  compilation,  Zeitxhrift  fiir  Riologio,  vol.  3,  p.  5. 


EFFECT   OF   SURPLUS   OF   PROTEIN. 
Daily  protein  katabolixm  of  dog — Bischoff  and  Volt. 


79 


Dates. 

Meat 
paten. 

Nltropen 
of  feed.  i 

Nitrogen 
excreted  in 
urine.2 

Nov.  20  to  27,  1858  

drums. 

170 

Grama. 
0  0 

Gram^. 
I9  6 

Nov.  24  to  25  

300 

10.2 

14  9 

May  1  to  4,  1804 

480 

10  3 

10  3 

Apr.  20  to  June  1  ,  1803  

500 

17  0 

18  7 

Nov.  22  to  23,  1855  

000 

20.4 

22  9 

Feb.  13  to  17,  1805  .. 

800 

27  2 

20  1 

Nov.  20  to  21,  18.58.. 

900 

30  0 

31  7 

Apr.  14  to  20,  1803  

1  ,000 

34.0 

35  9 

Nov.  IS  to  19,  18.58  

1,200 

40.8 

41.1 

Apr.  1  to  14,  1803..     . 

1  500 

51  0 

49  5 

Mar.  25  to  Apr.  1  ,  1859  

1,800 

61.2 

59  7 

Apr.  5,  1858 

1  900 

t>4  6 

04  9 

June  21  to  29,  1803  

2  000 

08  0 

07  ° 

Jan.  22  to  25,  1858  -.  

2,200 

74.8 

71  9 

Dec.  5  to  7,  1858.. 

2  500 

85  0 

80  7 

Jan.  25,  1858  

2.0CO 

90  4 

84.5 

Moreover,  what  lias  been  shown  to  be  true  of  an  exclusively  protein  diet  is 
substantially  true  also  of  one  containing  liberal  amounts  of  fats  or  carbo- 
hydrates. Thus  in  the  following  selection  from  Bischoff  and  Voit's  experiments1 
bearing  upon  this  point  it  is  clear  that,  notwithstanding  the  presence  of  con- 
siderable amounts  of  fat  in  the  feed,  the  protein  katabolism,  as  measured  by 
the  urinary  nitrogen,  increased  substantially  in  the  same  ratio  as  the  protein 
supply. 

DaiJy  protein  katalolism  of  dog — Bischoff  and   Voit. 

~  ~ i 


F 

eed. 

Nitroeen        T'rinarv 

Fat. 

Lean  meat. 

of  feed.2       nitrogen.3 

Nov.  22  to  Dec.  1,  18.57                     

Grams. 
2.50 

Grams. 
150 

Grams.          Gram.'. 
.5.1  ,                 7.3 

Dec.  2,  1S57       

250 

250 

8.  5                    8.  9 

Dec  5  1857   to  Jan   5   18,58 

250 

500 

17  0                   144 

Jan.  9  to  1  1  ,  18o8  

250 

1.000 

34.0                   28.3 

Jan   15  to  18,  1858 

250 

1.500 

51.0  |               45.9 

Apr.  1  to  7,  1859  

250 

1,800 

61.2  i               5C.  4 

Jan  13  to  14,  1859 

2.50 

2.000 

08.0  '                03.4 

Carnivorous  animals  have  been  extensively  used  in  the  investigation  of  such 
questions  as  the  foregoing,  and  others  which  are  to  be  discussed  later,  largely 
because  with  them  it  is  possible  to  employ  a  diet  consisting  of  but  one  or  two 
simple  nutrients,  but  the  main  facts  which  have  been  brought  out  by  such  in- 
vestigations have  been  shown  to  be  true  also  of  herbivorous  animals.  In  the 
latter,  as  in  the  carnivora.  the  protein  katabolism  is  determined  chiefly  by  the 
supply  of  protein  in  the  feed. 

As  early  as  1S."2,  eight  years  before  the  publication  of  Bischoff  and  Voit's 
inevstigations,  Lawes  and  Gilbert,4  in  discussing  the  results  of  theri  fattening 
experiments  upon  sheep  and  pigs,  called  attention  to  the  very  wide  variations 

1  Gesetzo  der  Erniihning  des  Fleischfressers.    ISGO,  pp.  07-115. 

2  Average  of  nitrogen  of  loan  moat,   15.4   per  font. 

3  Computed  from  urea. 

*  Report  British  Association  for  the  Advancement  of  Science,  1852,  Rothamsted 
Memoirs,  Vol.  II. 


80 


MAINTENANCE    RATIONS    OF    FARM   ANIMALS. 


in  the  «'i mount  of  protein  consumed,  both  per  unit  of  weight  and  especially 
per  unit  of  gain,  and  concluded  that  the  apparent  excess  of  protein  in  some 
cases  must  have  served  substantially  for  respiratory  purposes. 

Of  the  numerous  later  and  more  specific  investigations  on  herbivora  in  which 
the  nitrogen  excretion  has  been  determined,  the  following1  may  serve  as  an 
example.  Two  sheep  were  fed  in  periods  1  and  7  a  basal  ration  of  hay  and 
barley  meal.  To  this  ration  were  added  in  the  intermediate  periods  varying 
amounts  of  nearly  pure  protein  in  the  form  of  conglutin  (of  lupins)  or  of 
flesh  meal.  A  comparison  of  the  nitrogen  digested  from  the  ration  with  the 
urinary  nitrogen  shows  that  the  latter  increased  and  diminished  substantially 
parallel  with  the  former. 

Protein  lea  t  aboil  is  in  of  sheep  per  day  and  head — Ilenncberg  and  Pfeiffer. 


Sheep  I. 

Sheep  II. 

Nitrogen 
digested. 

Nitrogen 
in  urine. 

Nitrogen 
digested. 

Nitrogen 
in  urine. 

Period  1 

Grams. 

8.18 
17.80 
27.22 
36.  99 
26.76 
17.62 
8.34 

Grams. 
7.48 
16.82 
25.75 
32.71 
25.63 
16.  64 
8.06 

Grams. 
7.81 
17.72 
27.33 
37.07 
26.91 
16.94 
8.00 

Grams. 
6.98 
16.37 
23.94 
32.09 
24.54 
15.99 
7.  62 

Period  2 

Period  3  

Period  4 

Period  5. 

Period  6  

Period  7 

UTILIZATION    OF   PROTEIN    LIMITED. 


That  the  mere  giving  of  protein  food  can  not  cause  a  large  storing 
up  of  protein  is  indeed  sufficiently  obvious  from  daily  experience. 
The  muscles  of  the  weakling  can  not  be  converted  into  those  of  the 
athlete  by  feeding  him  upon  a  meat  diet,  nor  the  small  man  increased 
in  size  by  a  very  abundant  protein  supply.  The  protein  tissues  of 
the  mature  animal  have  reached  their  natural  limit  of  size  and  con- 
sequently the  capacity  of  the  body  to  store  up  protein  is  limited.  In 
such  an  animal,  beyond  the  minimum  required  to  make  good  the 
necessary  katabolism  in  the  cells  protein  can  be  utilized  only  to  a 
small  extent  in  the  body  as  protein,  and  it  is  therefore  rapidly 
katabolized,  its  nitrogen  appearing  in  the  urine  as  urea  and  other 
familiar  end  products.  Nor  is  the  situation  essentially  different  in 
the  growing  or  the  milk-producing  animal.  While  these  animals  are 
able  to  utilize  considerable  amounts  of  feed  protein,  yet  the  limit  of 
this  utilization  is  set  by  the  normal  rate  of  growth  of  the  protein 
tissues  or  the  capacity  of  the  mammary  glands  to  manufacture  the 
casein  and  other  proteins  of  the  milk.  Any  surplus  of  protein  over 
the  amount  which  can  be  used  for  this  purpose  is  katabolized  pre- 
cisely as  is  a  surplus  over  the  very  small  demand  of  the  mature 
animal. 


and  PfViflVr.     Journal  fiir  Landwlrtschaft,  vol.  38,  p.  215. 


PROTEIN    AS    A    SOURCE    OF    ENERGY. 


81 


As  a  single  striking  example  there  may  be  cited  an  experiment  by  Jordan,1  in 
which  the  protein  supply  of  cows,  beginning  with  a  liberal  ration,  was  gradually 
diminished  to  about  one-half  and  then  gradually  increased  again  to  the  original 
amount.  The  following  table  shows  the  average  nitrogen  balance  of  cow  Xo.  12 
of  the  second  series  of  experiments,  the  daily  results  being  grouped  into  periods 
as  indicated. 

Awrngc  dnili/  nitrogen  bnlancc  of  coir* — Jtinlnn. 


Pate. 

Number 
of  days. 

Nitrogen 
digested. 

Nitrogen 
of  milk. 

Nitrogen 
of  urine. 

Gain  by 
body." 

Jan. 
f>h 

30  to  Feb.  0  
6  to  10 

10 

Gram*. 
1SO.I5 
Iso  2 

drums. 

SI.  7 
81  4 

(jrams. 

87.0 
87  5 

Grams. 
+  17.9 
+  10  3 

Fob 

10  to  20.  . 

10 

1  01.  6 

77  5 

81  9 

+  2  2 

Feb 

26  to  Mar.  8 

JO 

130  8 

71  0 

+      3 

Mfir 

8  to  IS.  . 

10 

117  2 

GO  0 

43  7 

+  o  9 

Mar 

18  to  28  

10 

143.6 

09  0 

01  8 

+  1''  2 

Mir 

28  to  Apr.  7 

10 

171   4 

71  0 

89  2 

+  10  0 

Apr 

7  to  14.  ... 

7 

18.').  7 

71  9 

104  4 

+  94 

The  amount  of  milk  protein,  like  the  total  milk  solids,  diminished  in  quite  a 
normal  way  with  the  advance  in  lactation,  while  the  percentage  of  protein  in 
the  solids  remained  about  the  same.  On  the  low  protein  rations  of  the  middle 
periods  there  seems  to  have  been  some  falling  off  in  the  amount  of  milk  protein 
produced  (and  of  the  total  milk  solids  as  well)  in  comparison  with  what  might 
have  been  expected  on  an  unchanged  ration,  but  the  difference  is  small,  except 
in  one  or  two  periods  where  the  protein  supply  reached  the  lowest  limit.  Aside 
from  this  the  principal  effect  of  the  variations  in  the  amount  of  digestible  pro- 
tein supplied  was  to  increase  or  diminish  the  amount  of  urinary  nitrogen,  which, 
as  the  table  clearly  shows,  rose  and  fell  with  the  supply  of  nitrogen  in  the  feed. 

PROTKIX   AS   A   SOt'RCK   OF   KNKKCY. 

This  increased  katabolism  of  protein,  however,  is  not  to  be  re- 
garded as  a  total  loss  of  so  much  food  material.  The  manner  in 
which  surplus  protein  is  disposed  of  is  rendered  clear  by  a  considera- 
tion  of  the  chemistry  of  protein  katabolism.  Proteins  are  resorbed 
from  the  digestive  tract  in  the  form  of  comparatively  simple  cleav- 
age products,  chiefly  amino-acids,  and  the  body  uses  these  nitroge- 
nous cleavage  products  as  building  stones  out  of  which  to  reconstruct 
body  proteins  broken  down  in  the  vital  processes.  As  has  just 
been  shown,  however,  this  necessary  demand  is  relatively  small,  while 
the  mature  animal  has  lost  the  capacity  which  it  had  during  growth 
of  building  up  large  amounts  of  new  protein  tissue.  When  the 
blood  is.  so  to  speak,  flooded  with  these  amino-acids  in  high  protein 
feeding,  some  increase  in  the  formation  of  body  protein  appears  to 
result.  a>  will  be  shown  immediately,  but  this  consumes  a  relatively 
small  proportion  of  the  nitrogenous  matter  and  lasts  for  only  a 
limited  time.  It  is  obviously  an  advantage  to  the  organism,  there- 
fore, to  be  able  to  dispose  of  the  surplus  nitrogen.  This  it  accom- 
plishes by  splitting  off  the  XII,  group  and  excreting  it  in  the  form 

1  New  York  A?rrkMilUir;il  Experiment  Station.  Bulletins  132  and  107. 
848!.)°— Bull.  1-tt—  1 12 0 


82 


MAINTENANCE    RATIONS    OF    FARM    ANIMALS. 


of  urea,  etc..  leaving  a  nonnitrogenous  residue  which  contains  the 
larger  portion  of  the  chemical  energy  of  the  protein  which  it  repre- 
sents and  is  in  condition  to  be  oxidized  as  fuel  material.  (Compare 
pp.  30-32.) 

The  increased  nitrogen  excretion  on  a  high  protein  diet  is  simply 
the  method  by  which  the  organism  gets  rid  of  useless  nitrogen,  while 
retaining  the  larger  share  of  the  energy  of  the  protein  for  fuel 
purposes.  In  other  words  the  organism  when  confronted  with  a 
protein  supply  in  excess  of  its  needs  is  able  by  what  seems  to  be  a 
comparatively  simple  process  to  transform  it  into  nonnitrogenous 
fuel  material  with  but  slight  loss,  getting  rid  of  the  useless  nitrogen 
as  urea  through  the  urine.  The  increased  nitrogen  excretion  conse- 
quent on  high  protein  feeding  does  not  mean  the  total  destruction 
of  the  corresponding  amount  of  protein,  but  simply  its  transforma- 
tion into  compounds  which  can  serve  as  sources  of  energy. 

STORAGK   OF   PROTEIN. 

In  the  mature  animal  a  surplus  of  feed  protein  is  largely  katabo- 
lized,  so  that  a  continued  increase  of  the  protein  tissue  of  the  animal 
can  not  be  brought  about,  as  can  that  of  the  adipose  tissue,  simply 
by  a  surplus  in  the  feed.  The  protein  content  of  such  an  animal, 
however,  is  not  to  be  regarded  as  absolutely  fixed,  so  that  the  protein 
supply  has  no  effect  upon  it.  On  the  contrary,  a  considerable  range 
of  variation  is  possible. 

When  the  protein  supply  is  increased,  nitrogen  equilibrium  is  not  established 
at  once,  but  for  a  time  more  or  less  storage  of  nitrogenous  material  takes  place. 
For  instance,  when  a  dog  in  Yoit's  experiments1  was  changed  from  a  ration 
of  500  grains  of  meat  daily  for  42  days  to  one  of  l.r>00  grains,  the  urinary  nitro- 
gen showed  the  following  behavior  on  the  last  three  days  of  old  feeding  and  on 
the  first  seven  of  the  new: 


Dati 

.     ,    Meat  fed. 

Nitrogen 
of  feed. 

Nitrogen 
of  urine.2 

Gain  of 
nitrogen. 

18G3 
[May 

Experiment  Xo.  40                                              <Mav 

Grams. 

2!t                   500 
30  '                 500 

(frams. 
17.0 
17.0 

Grams. 
18.9 
18.2 

Grams. 
-1.9 

-1. 

|May 
[Juiie 
Juno 
(Juno 
Experiment  Xo.  41  •(June 

:-!i               500 

1                1,500 
2              1,500 
3               1,500 

4               1,500 

17.0 
51.0 
51.0 
51.0 
51.0 

17.7 
41.1 
44.  1 
40.  9 

48.0 

-  .7 

+9.'.) 
+0.9 
+  4.1 
+3.0 

June 
June 
June 

f.               1  .  500 
ti               1,500 
7             '  1  .  500 

51.0 
51.0 
51.0 

48.6 

48.9 
50.  (i 

+  2.4 
+  2.1 
+  .4 

1*1  »on   the  lighter  ration   the  animal   was  losing  a   small  amount   of  protein 
dailv.     On   the  heavier  ration   there  was  a   diminishing  gain   for  six   days,  ap- 


1  /••itsrln-il't   I'iir  liioln^ic.  vol.  :i.  p.  so. 
-  romputf]   fn»m  Voit's  figures  for  im-:i. 


FLUCTUATIONS   IN    BODY   PROTEIN. 


83 


proximate  equilibrium  being  reached  on  the  seventh  day.  The  total  gain  in  the 
seven  days  was  28.8  grams  nitrogen,  equivalent  to  847  grams  of  fresh  flesh,  or 
about  12  per  cent  of  the  surplus  fed,  equivalent  to  from  3.5  to  4  per  cent  of  the 
amount  probably  present  in  the  body  of  the  35-kilogram  dog. 

In  order  to  retain  this  protein  which  was  stored  up  in  the  body,  however,  it 
was  necessary  to  continue  the  heavier  ration  of  1,500  grams  of  meat.  When, 
in  previous  periods  of  the  same  scries,  a  ration  of  1,500  grams  of  meat  was  fol- 
lowed by  one  of  1,000  grams  and  this  by  one  of  500  grams,  the  protein  pre- 
viously stored  up  was  rapidly  katabolized  again,  as  the  following  table  shows: 

Loxx  of  protein  bij  dof) — Volt. 


Date. 

Meat  fed. 

Nitrogen 
of  feed. 

NitrocPii 
of  urine.1 

Gain  of 
nitrogen. 

Experiment  No  38  (last  3  day«) 

1803. 
Apr.  11 
Apr.   12 

Grams. 
1,500 
1,500 

Grams. 
51.0 
51.0 

Grams. 
48.  4 
50  9 

Grams. 
+2.« 
4.     1 

Experiment  No.  39  

Apr.   13 
Apr.  14 
Apr.  15 
Apr.  16 

1,500 
1,000 
1,000 
1,000 

51.0 
34.0 
34.0 
34.0 

/•.?.  8 
3S.G 
30.  4 
30.4 

-1  8 
-4.6 
-2.4 
-2.4 

Experiment  No.  40  . 

Apr.  17 
Apr.  18 
Apr.  19 
Apr.  20 
Apr.  21 
Apr.   22 

1,000 
1.000 
1,000 
500 
500 
500 

34.0 
34.0 
34.0 
17.0 
17.0 
17.0 

3C.  1 
34.3 
35.2 
23.7 
20.4 
20.9 

—  2.1 
-  .3 
-1.2 

-6.7 
-3.4 
-3.9 

Apr.  23 
Apr.  24 
Apr.  25 

500 
500 
500 

17.0 
17.0 
17.0 

18.8 
17.4 

18.8 

—  1.8 
-  .4 

-1.8 

The  total  loss  of  nitrogen  from  the  body  for  the  12  days  included  in  the 
table  is  31  grams,  or  an  amount  about  equal  to  that  stored  up  in  passing  from 
the  500-gram  to  the  1,500-gram  ration. 

This  comparatively  small  store  of  rapidly  katabolizable  protein  in  the  body 
after  liberal  protein  feeding  Voit  designated  as  circulatory  protein,  in  distinc- 
tion from  the  large  mass  of  stable  protein  which  lie  called  organ  protein.  A 
variety  of  other  names,  corresponding  to  more  or  less  definite  theories  as  to 
the  nature  of  the  distinction  between  the  two  types  of  protein,  have  been  pro- 
posed by  later  investigators,  such  as  stable  and  labile,  organized  and  unorgan- 
ized, tissue  and  reserve,  living  and  dead,  protein.  Si  ill  others,  notably  Gruber,1 
explain  the  temporary  storage  of  nitrogenous  matter  in  the  body  as  due  to  a 
lag  in  the  katabolisru  of  protein,  so  that  the  splitting  off  of  its  nitrogen  is  not 
complete  within  the  ordinary  24-hour  period.  The  facts,  however,  that  the 
nitrogen  excretion  follows  in  general  the  supply  in  the  feed  liul  that  a  tempo- 
rary and  limited  storage  of  nitrogenous  material  in  the  body  may  result  from 
liberal  protein  feeding,  are  undisputed. 

FLUCTUATIONS   IN    BODi"  PROTK1N. 

It  is  a  familiar  fact  that  a  fasting  animal  may  live  and  continue, 
to  perform  the  essential  bodily  functions  for  some  time,  while  los- 
ing daily  a  not  inconsiderable  amount  of  protein.  To  cite  a  :» ingle, 
striking  example,  Rubner  observed  in  a  fasting  rabbit  up  to  the  time 
of  death,  on  the  nineteenth  day.  a  loss  of  45.2  per  cent  of  the  com- 
puted nitrogen  of  the  body.3  While  this  is  an  extreme  case,  neverthe- 

1  ('ompul.-d   from   nron. 

2/citsohrift   fiir  ttiol.vi.\   vi.l    41'.  \>.  4(i7. 

•"K.  Voit.     Zoitschrift  fiir  P.iologie,  Vol.  41.  p.   ].".0. 


84  MAINTENANCE   RATIONS    OF    FAEM    ANIMALS. 

less  it  is  evident  that  there  must  be  a  relatively  large  loss  of  body 
protein  in  those  more  moderate  cases  in  which  the  deprivation  of 
protein  is  not  continued  so  long  as  to  cause  death.  Furthermore, 
the  losses  occurring  in  these  latter  cases  may  be  made  good  by  subse- 
quent feeding  and  the  animal  restored  to  its  original  state.  Strik- 
ing examples  of  the  same  fact  are  familiar  in  the  human  subject  in 
the  emaciation  due  to  long  illness  and  the  restoration  of  the  body 
during  convalescence.  Pugliese  *  has  shown  that  a  similar  storage  of 
protein  takes  place  rather  rapidly  in  the  liver  when  a  previously 
fasted  animal  receives  feed  again.  In  brief,  it  is  evident  that  the 
body  of  the  mature  animal  may  fluctuate  within  somewhat  wide  limits 
as  regards  its  protein  content  without  necessarily  causing  any  serious 
or  permanent  derangement  of  its  functions. 

"We  can  hardly  suppose  such  a  fluctuation  to  consist  to  any  large 
extent  of  an  actual  destruction  and  rebuilding  of  the  cells  of  muscu- 
lar or  other  tissue,  but  must  regard  it  as  effected  chiefly  by  changes  in 
the  amount  of  cell  contents — an  alternate  atrophy  and  hypertrophy  of 
the  cells  under  the  influence  of  the  changing  protein  supply.  This 
same  conception  may  be  invoked,  however,  to  explain  small  as  well 
as  large  fluctuations  in  the  body  protein.  According  to  Rubner,2 
the  cells  of  the  body  seek  to  maintain  an  optimum  protein  content, 
and  in  proportion  as  this  becomes  reduced  they  show  a  capacity 
for  storing  up  protein,  when  a  more  abundant  supply  is  offered  in 
the  feed,  which  is  analogous  to  that  observed  during  growth.  On  the 
other  hand,  when  the  supply  of  feed  protein  is  insufficient,  protein 
previously  stored  may  be  katabolized. 

In  other  words,  as  regards  its  stock  of  nitrogenous  material  the 
organism  may  exist  and  function  at  a  higher  or  lower  level  accord- 
ing to  the  amount  of  protein  supplied  in  the  feed,  while  for  each 
level  of  protein  stock  a  certain  supply  in  the  feed  is  necessary — that 
is,  the  protein  required  for  maintenance  varies.  With  carnivora  on 
a  large! v  protein  diet,  such  as  was  used  in  Voit's  experiments,  the 
adjustment  of  the  body  to  the  protein  supply  seems  to  take  place 
rather  promptly.  In  the  case  of  herbivora,  however,  the  adjustment 
appear.-*  to  be  more  gradual,  possibly  owing  to  the  relatively  large 
supply  of  nonnitrogenous  ingredient.-  in  their  feed,  and  apparently 
some  gain  of  protein  may  continue  for  a  considerable  time,  although 
when  expressed  as  a  percentage  of  either  the  total  feed  protein  or 
of  the  body  protein  the  gain  i-  relatively  small. 

KF.LATTON     TO     F.NKRCY     SUPPLY. 

The  prime  demand  of  the  organism  is  for  energy  for  the  per- 
formance of  its  vital  functions,  and  if  necessary  it  will  draw  upon 
its  own  tissues  for  this  purpo>e.  X<>  clear  conception  of  the  laws 

1  .Talm'slicrieht  iiln-r  die  Fortsohnt1r>  d'-r  Ticr-Cliemio,  vol.  .".4.  p.  r,^'.). 
2I>as   Probli-in   dor  I.obormlnu'T,   olc. 


RELATION    TO    ENERGY    SUPPLY.  85 

governing  the  protein  metabolism  can  be  reached   without    taking 
into  consideration  the  energy  relations. 

Ordinarily,  the  nonnitrogenous  nutrients  of  the  feed  constitute 
the  principal  source  of  this  energy.  The  proteins,  however,  or  at 
least  the  cleavage  products  of  their  digestion  or  transformation, 
readily  undergo  a  process  of  deamidization  by  which  their  nitrogen 
is  split  off  and  excreted,  leaving  a  nonnitrogenous  residue  which  is 
available  as  a  source  of  energy.  It  is  evident,  then,  that  the  rela- 
tive abundance  or  scarcity  of  the  supply  of  nonnitrogenous  nutrients 
to  the  cells  of  the  body  may  profoundly  modify  the  extent  and 
character  of  the  protein  metabolism  and  consequently  the  magnitude 
of  the  protein  requirement. 

One  instance  of  this  effect  is  the  so-called  premortal  rise  of  the 
protein  katabolism  of  the  fasting  animal  when  the  store  of  body 
fat  is  reduced  below  a  certain  level.  (Compare  pp.  12-13.)  Here 
the  relative  deficiency  of  fuel  material  in  the  circulation  causes  an 
increased  breaking  down  of  the  cell  protein,  presumably  by  hydro- 
lytic  cleavage  and  subsequent  deamidization,  its  nitrogen  being 
gotten  rid  of  as  urea,  etc.,  and  the  nonnitrogenous  residue  serving  as 
a  source  of  energy  in  place  of  the  lacking  fat. 

A  precisely  similar  thing  occurs  when  the  nonnitrogenous  nutri- 
ents in  the  feed  are  relatively  deficient  and  is  especially  striking  in 
their  entire  absence.  It  was  pointed  out  on  pages  75-78  that  the 
protein  katabolism  during  fasting  is  at  least  an  approximate  measure 
of  the  minimum  protein  requirement  of  the  body,  and  that  if  this 
amount,  or  perhaps  even  less,  be  supplied  in  the  feed,  along  with 
an  abundance  of  nonnitrogenous  material,  the  stock  of  protein  in 
the  body  may  be  maintained.  But  if  the  experiment  be  made  of 
supplying  the  minimum  of  protein  without  nonnitrogenous  matter 
a  very  different  result  is  obtained. 

Thus  in  one  such  experiment  by  E.  Voit  and  Korkunoff,1  a  fasting  dog 
excreted  about  4  grams  of  nitrogen  per  day,  equivalent,  of  course,  to  a  daily 
loss  of  about  24  grams  of  body  protein,  while  in  addition  to  this  it  must 
have  been  oxidizing  considerable  body  fat.  When,  however,  it  was  fed  slightly 
more  than  24  grams  of  protein2  (4.1  grams  nitrogen),  with  no  other  feed, 
its  nitrogen  excretion  jumped  to  n.HO  grams  per  day,  so  that  it  was  still  losing 
daily  1.4<i  grams  of  nitrogen,  equivalent  to  8.70  grams  of  protein.  Instead  of 
the  entire  amount  of  protein  in  the  feed  being  applied  to  make  good  the  losses 
of  protein  tissue,  over  one-third  of  it  was  katabolized,  its  nitrogen  appearing 
in  the  urine  and  its  nonnitrogciious  residue  doubtless  being  used  as  fuel 
material.  Protein  rather  more  than  equal  to  the  S.70  grams  lost  was  then 
added  to  the  ration,  but  again  the  protein  katabolism  increased  and  the 
body  failed  to  maintain  its  stock  of  protein,  and  it  was  not  until  protein  equal 
to  about  three  times  the  fasting  katabolism  was  fed  that  equilibrium  was 
reached.  The  details  of  the  experiments  are  shown  in  the  following  table. 

1  Zeitschrift   fiir  liiologie,   vol.   32,   p.   07. 

:  In  the  form  of  loan  meat  from  which  the  extractives  had  been  removed  by  treatment 
with  water. 


86 


MAINTENANCE   RATIONS    OF    FARM    ANIMALS. 


the  results  furnishing  also  a  striking  illustration  of  the  interesting  relations 
between  protein  supply  and  protein  katabolism  which  had  been  demonstrated 
more  than  30  years  earlier  by  the  classic  experiments  of  Bischoff  and  Voit. 

Effect  of  protein  supply  on  protein  katabolism  of  dog — E.  Voit  and  Korku  no  ff. 

Nitrogen  in — 


Food. 

Feces  and 
urine. 

Gain   (  +  ) 
or  loss(  —  ). 

Grams. 
Nothing  0 

Grams. 
3.996 

Grams. 
-3.996 

Extracted  meat  (grams): 
100  4.10 

5.558 

—  1.458 

140                                                                                                                             5.  74 

6.495 

—  .755 

165  .                                                                                                                         6.77 

7.217 

—  .447 

185  7.59 

7.804 

-  .214 

200                                                                                                                             8.  20 

8.726 

—  .526 

230.            10.24 

10.  579 

-  .339 

360  11.99 

12.052 

-  .ot;2 

410  .              .   .                                                             15.  58 

14.314 

+  1.266 

360  13.  68 

13.  022 

+  .058 

It  is  clear  that  in  the  protein-fed  animal,  as  in  the  fasting  animal, 
the  demands  of  the  organism  for  energy  take  precedence  over  the 
Deed  for  repair  material,  and  that  in  default  of  nonnitrogenous 
material  the  protein  of  feed  or  of  tissue  is  seized  upon  and  katabo- 
iized  for  this  purpose  even  at  the  expense  of  a  loss  of  body  protein, 
the  body  seeming  to  find  it  easier  to  do  this  than  to  draw  upon  the 
stores  of  fat  in  the  adipose  tissues. 

What  is  so  strikingly  true  in  the  total  absence  of  nonnitrogenous 
nutrients  holds  good  also  in  less  degree  in  case  of  their  relative  de- 
ficiency. If  a  portion  of  the  nonnitrogenous  nutrients  are  withdrawn 
from  a  mixed  ration,  the  protein  katabolism  usually  increases,  while, 
on  the  other  hand,  if  nonnitrogenous  nutrients  be  added  to  such  a 
ration  the  tendency  is  to  diminish  the  protein  katabolism.  This 
well-known  influence  of  the  supply  of  nonnitrogenous  nutrients  upon 
the  protein  katabolism,  even  in  an  abundant  ration,  is  well  illustrated 
by  some  of  Kellner's  respiration  experiments  on  cattle,1  in  which 
starch  was  added  to  a  basal  ration.  The  following  table  shows  the 
average  daily  gain  of  nitrogen  by  the  animal  on  the  basal  ration  and 
die  increased  gain  following  the  addition  of  starch. 

Kffcct  of  nonnitrot/cnous  nutrient*  on   i/nin   of  protein-   Inj  cattle — Kclhicr. 


Gain  of  nitrogen. 


Animal. 

On  basal 
ration. 

With  addi- 
tion of 
starch. 

Difference. 

Grams. 
Ox  D  12.  75 

Grams. 
13.71 

GramK. 
+  0.95 

Ox  F                                                                                                                               5  64 

20  37 

+20.  73 

Ox  f!                                                                                                                              -.03 

17.  09 

+  17.12 

Ox  1  r                                                                                                                               7.  23 

12.  95 

+  5.72 

OK  J  .                                 5.49 

15.05 

+  9.56 

1  Die    Landwirtschaftllchcn    Versuchs-Statlonen.    Band   53. 


RELATION    TO   ENERGY   SUPPLY.  87 

It  has  been  shown  that  this  effect  is  produced  not  only  by  the  true 
fats  and  by  the  soluble  hexose  carbohydrates,  such  as  starch  and  the 
sugars,  but  likewise,  in  the  case  of  herbivorous  animals,  by  those  ill- 
known  ingredients  of  feeding  stuffs,  especially  of  the  crude  fiber  and 
the  nitrogen-free  extract,  which  disappear  in  the  passage  of  the  food 
through  the  alimentary  canal  and  which  are  commonly  spoken  of  as 
being  digested.  This  statement  covers  also  the  organic  acids,  whether 
resulting  from  the  fermentation  of  the  carbohydrates  or  contained 
in  the  feed.1 

We  are  not,  however,  to  conceive  of  a  sharp  distinction  in  this 
respect  between  an  insufficiency  and  a  sufficiency  of  nonnitrogenous 
nutrients,  but  rather  of  a  tendency  on  the  part  of  the  latter  to 
diminish  the  protein  katabolism,  a  tendency  more  or  less  marked 
according  to  their  abundance  in  the  ration.  We  are  not  to  under- 
stand that  no  nitrogenous  material  is  katabolized  for  fuel  purposes 
as  long  as  sufficient  nonnitrogenous  nutrients  are  present  to  supply 
the  demands  for  energy,  nor  that  even  the  largest  quantities  of 
the  latter  can  prevent  the  katabolism  of  protein  supplied  in  excess 
of  the  possible  constructive  use  by  the  body.  We  may  believe  that 
the  protein  cleavage  products,  either  derived  from  the  feed  or  from 
tissue  katabolism,  are  always  present  in  the  blood  and  that  more  or 
less  deamidization  is  continually  going  on,  resulting  in  a  use  of 
protein  material  as  fuel.  On  the  other  hand,  nonnitrogenous  sub- 
stances, derived  from  the  feed  or  the  body  fat,  are  also  present  and 
take  their  share  in  supplying  energy.  We  may  probably  conceive 
of  the  quantitative  character  of  the  katabolism  as  being  determined, 
in  a  very  broad  sense,  by  the  law  of  mass  action.  An  increase  of  non- 
nitrogenous  materials  in  the  blood  or  lymph  tends  to  diminish  the 
deamidization  and  subsequent  oxidation  of  the  cleavage  products 
of  protein  and  through  this,  secondarily,  to  diminish  the  breaking 
down  of  body  protein  or  to  stimulate  and  prolong  the  limited  storage 
of  protein  possible  in  the  mature  animal. 

As  regards  the  maintenance  requirement,  it  is  evident,  then,  that 
the  sufficiency  of  a  given  amount  of  protein  depends  not  only  upon 
the  plane  of  protein  nutrition  of  the  body,  but  also  upon  the  amount 
of  nonnitrogenous  nutrients  supplied  with  the  protein.  With  an 
abundant  supply  of  the  former  an  amount  of  protein  equal  to  the 
fasting  katabolism,  or  perhaps  even  less,  appears  to  be  a  sufficient 
minimum  for  maintenance.  As  the  supply  of  nonnitrogenous  ma- 
terials is  reduced  a  larger  supply  of  feed  protein  seems  to  be  required 
to  reach  equilibrium  because  more  and  more  of  it  is  diverted  for 
use  as  fuel,  so  that  in  the  total  absence  of  nonnitrogenous  nutrients 
a  large  excess  of  protein  must  be  fed  before  equilibrium  between  in- 
come and  outgo  is  reached.  In  interpreting  experiments  or  formulat- 

1  Compare  Armsby,  Principles  of  Animal  Nutrition,  pp.   IIT-TJT. 


88  MAINTENANCE   RATIONS   OF   FARM   ANIMALS. 

ing  a  maintenance  ration,  therefore,  it  is  not  sufficient  to  consider 
simply  the  amount  of  protein,  but  account  must  be  taken  of  the 
supply  of  nonnitrogenous  materials. 

VALUE  OF  NONPIJOTEIX. 

The  crude  protein  of  the  feed  of  farm  animals  includes  not  only 
true  protein  but  a  great  variety  of  other  nitrogenous  substances, 
grouped  for  convenience  under  the  designation  "  Xonprotein."  In 
considering  the  results  of  experiments  upon  the  protein  require- 
ments of  these  animals,  therefore,  it  is  necessary  to  determine 
whether  the  true  protein  should  be  the  basis  of  comparison  or 
whether  the  nonprotein  has  some  value  for  maintaining  the  protein 
tissues  of  the  body. 

The  wrriter  has  recently  l  considered  in  some  detail  the  experimen- 
tal evidence  on  this  point,  and  the  discussion  need  not  be  repeated 
here.  It  appears  to  have  been  demonstrated  by  recent  experimental 
results,  especially  by  those  of  Kellner,  Morgen,  and  the  Laboratory 
for  Agricultural  Research  in  Copenhagen,  that  the  nonprotein  of 
ordinary  feeding  stuffs  is  available  for  the  maintenance  of  rumi- 
nants, probably  indirectly  through  a  conversion  to  protein  by  means 
of  bacteria  in  the  digestive  tract.  On  the  other  hand,  investigations 
have  not  thus  far  shown  that  such  nonprotein  has  any  material  value 
for  production  purposes.  The  writer  therefore  reached  the  conclusion 
that  for  the  present,  pending  further  investigation,  it  is  desirable  to 
consider  ordinarily  only  the  digestible  true  protein  in  the  compu- 
tation of  rations  for  productive  purposes,  ignoring  the  nonprotein. 
This  implies,  however,  that  a  discussion  of  the  results  of  experi- 
ments upon  the  protein  requirement  shall  also  be  based  upon  the 
amounts  of  true  protein  supplied  and  not  upon  the  crude  protein. 
This  will  have  two  effects. 

First,  it  will  make  the  protein  requirement  appear  smaller  than  it 
really  is.  Suppose,  for  example,  that  a  series  of  trials  in  which  the 
ratio  of  digestible  nonprotein  to  digestible  protein  is  1 : 10  shows 
that  nitrogen  equilibrium  is  reached  with  a  ration  supplying  500 
grams  protein  and  50  grams  nonprotein.  Regarding  the  true  protein 
only,  the  maintenance  requirement  is  500  grains,  while  the  real  re- 
quirement of  the  animal  is  550  grams. 

In  the  second  place,  however,  this  error  will  be  largely  compensated 
for  when  the  actual  computation  of  rations  is  also  based  on  the  true 
protein.  Thus  in  the  case  just  supposed,  if  a  maintenance  ration 
be  computed  from  any  feed  or  mixture  in  which  the  ratio  of  non- 
protein  to  protein  is  the  same  as  in  the  experiments  from  which  the 
maintenance  requirement  was  deduced,  viz,  1:10,  it  is  obvious  that 
the  same  final  result  will  be  reached  whether  the  maintenance  require- 

1  Bureau  of  Animal  Industry,  Bulletin  1.'59. 


PROTEIN  REQUIREMENT  OF  CATTLE.  89 

ment  be  considered  to  be  500  grams  of  true  protein  or  550  grams  of 
crude  protein.  Only  when  the  proportion  of  nonprotein  to  true  pro- 
tein varies  widely  from  that  existing  in  the  rations  used  in  determin- 
ing the  protein  requirement  will  any  significant  error  arise  in  comput- 
ing rations. 

In  the  results  considered  on  succeeding  pages,  both  the  crude  pro- 
tein and  true  protein  of  the  rations  are  stated  when  these  are  given 
in  the  reports  of  the  experiments. 

MINIMUM  OF  PROTEIN   FOR  FA  KM   ANIMALS. 

In  considering  the  protein  supply  of  different  species  of  farm 
animals,  it  is  important  to  distinguish  between  two  points  of  view. 
On  the  one  hand,  it  may  be  sought  to  determine  the  least  amount 
of  protein  upon  which  the  protein  tissues  of  the  animal  can  be 
maintained.  This  might  be  called  the  physiological  minimum.  It 
shows  the  proportion  of  protein  in  a  productive  ration  which  is  de- 
voted solely  to  maintenance.  On  the  other  hand,  the  endeavor  may 
be  to  formulate  the  most  advantageous  amount  of  protein  to  supply 
when  an  animal  is  actually  to  be  maintained  for  a  time  and  this 
amount  may  very  possibly  be  greater  than  the  physiological  mini- 
mum. The  first  point  of  view,  however,  is  plainly  the  fundamental 
one  and  should  receive  our  first  consideration.  Having  determined 
the  lower  limit  of  protein  supply,  it  will  then  be  possible  to  consider 
intelligently  the  advantages,  if  any,  of  a  surplus. 


For  obvious  reasons  it  is  impracticable  to  ascertain  the  fasting 
katabolism  of  ruminants;  their  maintenance  requirement  as  regards 
protein  must,  therefore,  be  determined  by  a  process  of  trial. 

The  earliest,  and  for  a  long  time  the  only,  determinations  of  the  maintenance 
requirements  of  cattle  were  those  of  Ilenneberg  and  Stohmann  in  1S5S,  the 
results  of  which  as  regards  energy  were  cited  on  page  39.  In  0  experiments 
the  minimum  amount  of  digestihle  crude  protein  (total  nitrogen  X  G.25)  sup- 
plied per  day  was  0.35  pound  per  l.ono  pounds  live  weight  and  this  quan- 
tity seemed  to  be  more  than  sullicient  for  maintenance.  On  the  average  of  the 
6  experiments,  in  2  of  which  there  was  some  loss  of  body  protein.  0.53 
pound  of  digestible  crude  protein  was  consumed  per  l.OoO  pounds  live 
weight.  Wolff's  standard  for  maintenance,  long  current,  viz,  0.7  pound  di- 
gestible crude  protein,  was  based  on  Ilenneberg  and  Stohmnnn's  experiments 
with  an  allowance  for  the  fact  that  their  experiments  were  made  at  a  relatively 
high  temperature.  Wolff's  standard,  however,  was  intended  as  a  guide  for 
actual  maintenance  feeding  rather  than  as  an  expression  of  the  minimum 
protein  requirement. 

In  the  light  of  later  experience,  the  methods  of  these  earlier  experiments 
must  be  considered  imperfect  and  their  results  are  now  chiefly  of  historical 
interest.  The  first  experiments  by  modern  methods  were  those  of  G.  Kiihn  and 


90 


MAINTENANCE   RATIONS   OF   FARM   ANIMALS. 


Kellner  at  the  Moeckern  Experiment  Station,1  which  include  determinations 
of  the  gain  or  loss  of  fat  as  well  as  of  protein  and  hence  afford  a  secure  basis 
for  judgment  as  to  the  sufficiency  of  the  energy  supply.  Including  subsequent 
slight  corrections  by  Kellner,2  the  principal  results  as  regards  protein  are  sum- 
marized in  the  following  table: 

Gain  or  loss  of  protein  bij  cattle — G.  Kiihu  and  Kellner. 


No.  of  animal. 

Live 
weight. 

Protein  per  day  and  1,000  pounds  live  weight. 

Digestible  in  feed. 

Gain  by 

animal. 

Crude 
protein.3 

True 
protein.4 

Protein. 

Fat. 

II 

Pounds. 
1,394 
1.393 
1,386 
1,327 
1,420 
1.481 
1,365 
1,348 

Pound. 
0.65 
.53 
.53 
.  75 
.71 
.SO 
.71 
.35 

Pound. 
0.5S 
.35 
.34 
.60 
.57 
.65 
.56 
.28 

Grams. 
-17.2 
-24.5 
-25.9 
+21.8 
+  11.8 
-  3.2 
+27.  2 
—65.3 

Grams. 
+  75.8 
+  63.0 
+  20.4 
+  106.6 
+  119.3 
+  71.7 
+  103.0 
-  78.0 

III. 

IV 

V      . 

VI... 

XX 

A  

B 

If  the  very  small  loss  of  protein  by  ox  XX  may  be  regarded  a:s  falling 
within  the  limits  of  experimental  error,  the  eight  experiments  may  be  averaged 
as  follows : 


Animal. 


Digestible  in  feed. 


Gain  bv  animal. 


Cmde 


protein.         protein 


True 


Protein. 


Fat. 


Animals  V,  VI,  XX,  and  A 

Animal  II 

Animals  III,  IV,  and  B 


Pound. 
0.74 
.65 
.47 


Pound. 
0.60 

.58 


Grams,     i     Grams. 

14.4  +100.2 

-17.2  !          +75.8 


-38.6 


+     5.4 


It  appears  that  approximately  O.G  pound  of  digestible  true  protein  or  0.74 
pound  of  crude  protein  per  1.000  pounds  live  weight  was  at  least  sufficient  to 
rather  more  than  maintain  nitrogen  equilibrium  when  the  total  energy  supply 
in  the  ration  was  sufficient  to  cause  a  small  gain  of  fat,  while  half  this  amount 
of  true  protein  or  0.47  pound  of  crude  protein  was  manifestly  insufficient.  A 
reduction  to  0.35  pound  digestible  true  protein  or  0.53  pound  digestible  crude 
protein  in  the  cases  of  ox  III  and  ox  IV,  even  with  a  sufficient  supply  of  non- 
nitrogenous  material  to  cause  some  gain  of  fat,  resulted  in  a  loss  of  protein 
from  the  body,  while  in  the  case  of  ox  B,  with  a  slightly  lower  supply  of  true 
protein  and  a  materially  lower  one  of  crude  protein  and  a  ration  materially 
below  the  maintenance  requirement,  the  loss  of  protein  was  still  greater.  The 
considerable  loss  of  protein  by  ox  II  is  not  readily  explicable. 

Experiments  upon  the  same  subject  were  also  made  by  the  writer5  in  1S92- 
189S,  chiefly  upon  rations  of  timothy  <ir  mixed  hay,  with  the  addition  in  Ex- 
periment VII  of  starch,  but  also,  in  Experiment  VIII.  upon  a  ration  consisting 

1  Die   Landwlrtscbaftlichen   Versuchs-Statlonen,   vol.   44,   p.  257  :   vol.   41 
-  IMe  KrniUminjr  der  Landwirtschaftllche  Xutztiero.  5th  ed.,  p.  411. 

3  Corrected  for  estimated  loss  of  nitrogen  in  drying  of  fecos. 

4  As  reported  in  the  original  account  of  these  experiments. 
1  Pennsylvania  Experiment  Station,  Bulletin  42,  p.  165. 


PROTEIN  REQUIREMENT  OF  CATTLE. 


91 


chiefly  of  grain  together  with  u  minimum  of  wheat  straw.    The  results  of  these 
experiments  are  contained  in  the  following  table : 

Nitrogen  balance  per  1,000  pounds  live  weight — Artnuby. 


Experiment. 

Digestible  in  feed. 

Nutritive 
ratiol: 

Gain  or  loss 
ofnitroKPii 
by  body. 

Crude 
protein. 

True 
protein. 

Experiment  I: 
Steer  1  

Pound. 
0.  30 
27 
.31 

.45 
.47 
.49 

.62 
.60 

.07 

.40 
.44 
.51 

.62 
.57 

.  06 

Pound. 
0.20 

.  23 
.27 

.38 
.40 
.42 

.59 
.55 
.63 

.31 

.20 
.30 

.52 

'.48 
.55 

20.  1 
20.4 
18.0 

13.4 
13.  0 
12.  8 

10.0 
10.9 
10.0 

23.0 
25.  3 
23.9 

10.4 
10.7 
10.0 

Grams. 
-2.7 
-   .4 
-1.2 

+1.9 

+  4.2 
+5.2 

+  4.7 

+  0.0 
+2.8 

+5.  7 
+3.7 
+  4.4 

+  .2 
„     1 

-2.0 

Steer  2 

Steer  3   

Experiment  II: 
Steer  1 

Steer  2  

Steer  3 

Experiment  VI: 
Steer  1  

Steer  2 

Steer  3 

Experiment  VII: 
Steer  1                  

Steer  2  

Steer  3 

Experiment  VIII: 
Steer  1 

Steer  2 

Steer  3                           

In  Experiments  II,  VI,  VII.  and  VIII  digestible  crude  protein  ranging  from 
0.44  to  O.G7  pound  fully  sufficed  for  maintenance,  with  a  single  exception.  The 
range  of  true  protein  was  somewhat  wider,  viz,  0.20  to  0.03  pound.  The  rations 
of  Experiment  VII  were  relatively  richer  in  nonprotein  than  were  those  of  the 
other  experiments,  and  the  adequacy  of  these  very  low  protein  rations  sug- 
gests a  utilization  of  the  nonprotein,  although  the  abundance  of  nonnitrogenous 
nutrients,  as  shown  by  the  nutritive  ratio,  may  also  be  a  factor.  The  rations 
of  Experiment  I  were  obviously  inadequate,  even  although  the  supply  of  non- 
nitrogenous  matter  was  liberal. 

Experiments  upon  a  steer  by  Armsby  a 'id  Fries1  in  which  the  respiratory 
products  were  determined  gave  results  in  general  accord  with  those  already 
cited.  Computed  per  1,000  pounds  live  weight,  these  results  were  as  follows: 

\Hroffcn-  balance  per  1,000  pounds  lire  ireifjltt — .\rmbsij  and  7-Y/r.v. 


Digestible. 


Gain  or  loss  bv  bodv. 


Crude 
;     protein. 

True 
protein. 

Nitrogen. 

Fat. 

1902.                                                    Pound. 
Period  A  0.  45 

Pound. 
0.  30 

Grams. 
—  9.  1 

Grams. 
—  2.XO.  5 

.42 

-  1.3 

—  89  2 

Period  C                           .53 

.44 

+       .6 

Period  D  .OS 

-  12.3 

4-    16.  S 

1903. 
Period  I                                                                                  !               .  00 

.40 

—  10.  4 

-192.9 

Period  II                                           .51 

.38 

-  15.  0 

-350.  S 

Period  III                                                                              '               .70 

.  53 

-2.3 

—  109.7 

Period  IV                                .97 

.84 

-t-  9.  2 

+  19''.  4 

1904. 
Period  I  '               .44 

.34 

-  9.5 

-312.7 

Period  11                                                                                               .74 

—       s 

—  75.2 

Period  III    .60 

.46 

_       5 

-155.4 

1  Bureau  of  Animal  Industry,  Bulletins  51,  74,  and  101. 


92 


MAINTENANCE   RATIONS   OF   FARM   ANIMALS. 


In  periods  C  and  D  of  1902  and  period  IV  of  1903,  the  only  ones  in  which 
maintenance  was  reached,  the  crude  protein  ranged  from  0.53  to  0.97  and  the 
true  protein  from  0.44  to  0.84.  In  a  later  series  of  experiments  l  on  two 
immature  steers,  from  0.92  to  1.13  pounds  of  crude  protein,  or  0.69  to  0.77 
pound  true  protein  per  1,000  pounds  live  weight  sufficed  for  maintenance  in 
three  periods  in  which  there  was  some  gain  of  fat.  The  experiments  furnished 
no  evidence  that  so  large  an  amount  was  necessary,  since  the  next  lowest 
amount  was  0.44  pound  crude  protein  or  0.37  pound  true  protein  in  a  ration 
producing  a  slight  gain  of  fat  but  a  small  loss  of  protein. 

The  investigations  of  the  Laboratory  for  Agricultural  Research  in  Copen- 
hagen upon  the  protein  requirements  for  milk  production  include  also  two  ex- 
periments on  dry  cows2  with  rations  furnishing  relatively  small  amounts  of 
digestible  nitrogenous  matter,  chiefly  in  the  form  of  true  protein.  The  periods 
in  which  an  approximate  nitrogen  balance  was  secured  gave  the  following  data  : 

Nitrogen  balance  of  dry  coirs  per  day  and  head — Copenhagen  experiments. 


Crude  protein 


Gain  of 

Cow  and  f-trriod. 

weight. 

Per  head. 

Per  1,000 
pounds 
live  weight. 

per  head 
by  animal. 

Cow  117: 
Period  2                       ...          

488 

Grama. 
87.5 

Pound. 
0.18 

Grams. 
-3 

Period  4 

485 

100.0 

21 

+2 

Cow  134: 
Period  1      

466 

143.8 

.31 

—5 

Period  4 

443 

112.5 

.25 

4-3 

The  experiments  on  milking  cows  also  afford  approximate  data  as  to  the  main- 
tenance requirement.  If  the  protein  of  the  milk  is  subtracted  from  the  total 
digestible  protein  of  the  feed,  the  remainder  is  obviously  the  maximum  amount 
which  was  available  for  maintenance.  In  Bulletin  139  of  this  bureau, 
pages  3S-39,  there  are  given  the  results  of  those  experiments  in  which  the 
smallest  amounts  of  protein  were  consumed.  Selecting  from  among  these  those 
in  which  there  was  an  approximate  nitrogen  equilibrium,  we  obtain  the  results* 
tabulated  below  : 

Daily  yuin  »r  M..«-,V  of  protein  bi/  coins — Copenhagen  experiments. 


Maximum 

Cow  ami  perio'i. 

Live 

weight. 

Crude 
protein 
digested. 

Protein 
of  milk. 

crude  pro- 
tein avail- 
able for 
mainten- 

Oiiin of 
protein  by 
animal. 

ance. 

Sixtieth  report: 

Kilos. 

Grams. 

Grams. 

Grams. 

Grams. 

Cow  No.  10.  pe  iod  C> 

44(1 

000.  0 

387.5 

212.5 

-12.5 

Cow  No.  53,  pe  iod  4 

454 

543.  8 

350.0 

193.8 

-12.5 

Cow  No  53.  pe  iod  (i 

451 

568.8 

306.  3 

262.  5 

+  18.8 

Cow  No.  08,  pe  iod  4 

4(il 

575.  0 

393.  8 

181.2 

-31.3 

Cow  No.  08,  pe  iod  1  1.  . 

441 

506.3 

312.  5 

193.8 

-12.5 

Cow  No.  58,  period  4.  .  . 

4S5 

531.3 

325.  0 

206.  3 

-  6.3 

Cow  No.  58,  period  0  

485 

581.3 

293.8 

287.5 

+  37.5 

Sixty-third  report: 

Cow  No.  <>8,  period  ti 

453 

575.  0 

368.  7 

206.3 

-25.  0 

I'.nrojui    of   Animal    Industry.    Rulli-tin    1  l^S. 
-  Sixty-third  Report,  pp.  128  and  30. 


PROTEIX  REQUIREMENT  OF  CATTLE.  93 

In  the  two  periods  in  which  there  was  a  Rain  of  protein  l»y  the  animal  the 
crude  protein  available  for  maintenance,  computed  per  l.ooo  pounds  live  weight, 

vvas:  Pound. 

Cow  No.  53,  period  0__  ._  0.58 

Cow  No.  58,  period  b'_ .  .  59 

In  the  four  periods  in  which  the  loss  of  protein  by  the  animal  did  not  exceed 
32.5  grams  (2  grams  nitrogen)  the  corresponding  amounts  were: 

Pound. 

Cow  No.  10,  period  G.__  .  0.48 

Cow  No.  53,  period  4__  .4.'! 

Cow  No.  08,  period  14 .44 

Cow  No.  58,  period  4 .  43 

These  results  are  quite  of  the  same  order  as  those  obtained  by  Kellner  and  by 
Armsby,  while  those  on  the  two  dry  cows  are  much  lower,  with  the  exception  of 
a  single  result  of  Arnisby's.  (Experiment  I,  steer  2.; 

In  drawing  conclusions  from  the  results  recorded  in  the  foregoing 
pages,  it  is  important  to  remember  that  what  it  is  sought  to  determine 
is  the  minimum  protein  requirement.  As  has  been  shown  on  previous 
pages,  an  excess  of  feed  protein  above  this  minimum  is.  in  the  case  of 
the  mature  animal,  substantially  all  katabolized,  producing  no  mate- 
rial gain  of  protein.  The  fact  of  an  equality  of  income  and  outgo 
of  nitrogen  upon  a  given  ration  of  protein,  therefore,  while  it  shows 
that  the  quantity  consumed  is  sufficient  for  maintenance  does  not 
show  that  a  smaller  amount  would  not  suffice.  What  we  have  to 
consider  is  the  evidence  of  the  experiments  regarding  the  least 
amount  sufficient  for  maintenance.  It  is  evident  that  this  minimum 
amount  is  relatively  small,  but  it  is  also  evident  that  the  recorded 
results  do  not  suffice  to  fix  with  certainty  the  absolute  minimum. 

The  lowest  recorded  amounts  per  1.000  pounds  live  weight  upon 
which  nitrogen  equilibrium  was  reached  were  0.21  pound  and  0.25 
pound  of  crude  protein  in  the  Copenhagen  experiments  on  dry  cows. 
while  almost  as  small  a  quantity,  viz.  0.27  pound  crude  protein  or  0.23 
pound  true  protein  in  Armsby "s  Experiment  I.  steer  2.  fell  very 
little  short  of  reaching  nitrogen  equilibrium.  Aside  from  these 
somewhat  exceptional  results,  the  lowest  figures  obtained  per  1.000 
pounds  live  weight  were  0.-13  pound  crude  protein  and  0.3*  pound 
true  protein.  The  maximum  is  found  in  Armsby  and  Fries'  experi- 
ment of  1Q03-4.  viz,  0.00  pound  crude  protein  and  O.S-t  pound  true 
protein,  but  it  seems  altogether  probable  that  the  animal  in  this 
period  was  consuming  a  surplus,  of  protein.  If  we  omit  these  few 
extreme  results  in  either  direction,  the  average  and  range  of  the 
results  of  the  other  experiments  are  as  follows: 

Arrragr  tnul  raiuje  of  protein  requirements  of  cullh. 


\umberof                I'rotPin  requirement. 

men  Is.     !    Average. 

Maximum. 

Minimum. 

Ofude  protein  .     .       .        

Pound. 

l!t  '                II.  5") 
1.'                    ..'.' 

Pound. 

M.  7.1 

.  <><l 

Pound. 
0.  4:! 
.38 

True  protein  .  .  . 

94  MAINTENANCE   RATIONS   OF   FARM   ANIMALS. 

It  seems  safe,  therefore,  to  estimate  0.6  pound  of  crude  protein  or  0.5 
pound  true  protein  per  1,000  pounds  live  weight  as  representing  in  a 
general  way  the  minimum  protein  requirement  of  mature  cattle  with  a 
probable  range  of  0.1  or  0.2  pound  either  way  under  varying  conditions. 

For  actual  maintenance  feeding  it  is  probable  that  a  somewhat 
more  liberal  supply  of  protein  than  is  indicated  by  these  figures 
would  be  advisable.  Rations  so  poor  in  protein,  if  containing  an 
adequate  amount  of  nonnitrogenous  matter,  would  probably  suffer  a 
loss  through  failure  of  the  animal  fully  to  digest  the  nonnitrogenous 
matter.  A  somewhat  narrower  nutritive  ratio  could  readily  be 
reached  in  practice  in  ordinary  feeding  Avithout  additional  expense 
and  from  the  standpoint  of  digestibility  would  very  likely  be  justified. 

SHEEP. 

While  a  considerable  number  of  experiments  with  sheep  are  on 
record  in  which  approximate  maintenance  as  a  whole  Avas  observed, 
at  least  so  far  as  could  be  judged  from  the  liATe  Aveight,  feAv  of  them 
afford  satisfactory  data  as  to  the  minimum  protein  requirement. 
For  the  immediate  purpose  of  this  discussion,  only  experiments  in 
Avhich  the  nitrogen  balance  Avas  actually  determined  are  available, 
mere  maintenance  of  Aveight  being  too  uncertain  a  criterion. 

A  distinct  difference  between  cattle  and  sheep,  which  affects  the  protein 
requirement,  lies  in  the  greater  demand  for  protein  incident  to  the  growth  of 
wool  in  the  latter  animals  as  compared  with  that  of  hair  in  the  former.  The 
results  of  determinations  by  Arnisby  and  Fries1  on  the  same  two  steers  in  two 
consecutive  winters  showed  an  average  production  of  epidermal  tissue,  includ- 
ing the  growth  of  hair  and  the  loss  in  brushings,  equivalent  to  0.19  gram  nitro- 
gen per  day  and  1.000  pounds  live  weight,  which  is  equal  to  0.0025  pound  pro- 
tein, an  amount  too  small  to  materially  affect  our  estimates  of  the  maintenance 
requirement.  In  the  case  of  sheep,  determinations  of  the  growth  of  wool  by 
several  investigators  afford  the  following  data  regarding  the  average  amount 
of  protein  required  for  this  purpose.  The  results  have  been  computed  per 
3.000  pounds  live  weight  for  the  sake  of  ready  comparison  : 

Protein  contained  in  daily  f/roictJi  of  irool  per  1,000  pound*  lire  u-eiglit. 

Pound. 

Ilenneberg.  Kern,  and  Wattenberg2 Mature  sheep--          ._  0.132 

Ilenneberg,   Kern,  and  Wattenberg3 Lambs__  .143 

Weifke4--  - (Jrowing  sheep •    .100 

Ilenneberg  and   Pfeiffer  5__  ..  Mature  sheep__  .140 

Pfeiffer  and  Kalb°__  __Mature  sheep. _  .150 


Average   .135 

Although,  as  the  foregoing  figures  show,   the  protein   requirements  of  sheep 
for  the  growth  of  wool  are  considerably  greater   than   those  of  cattle  for  the 

1  Bureau  of  Animal  Industry,  Bulletin   12S. 
-Journal  fiir  Landwirtscliaft,  vol.  L'G,  p.  540. 
"  Ibid.,  vol.  1'S,  p.   liSO. 

4  Lnndwirtschaflliehe  .Talirlniclior.  vol.  0,  p.  -05. 
•" •  .Journal  fiir  Landwirtscliaft,  vol.  .'18,  p.  L'15. 
"  Landwirtschaftliehe  Jalirbiiclier,  vol.  21,  p.  175. 


PROTEIN    REQUIREMENT   OF   SHEEP. 


95 


growth  of  hair,  the  absolute  difference,  after  all,  does  not  add  very  greatly  to 
the  total  maintenance  requirement. 

In  Henneberg  and  Stohmann's  Weende  experiments1  nr>on  two  sheep  fed 
exclusively  on  meadow  hay,  there  was  digested  on  the  average  per  1,000  pounds 
live  weight:  Pounds. 

Crude  protein  (total  N  X  G.25)__  _  1.  322 

Nitrogen-free  extract _  0.28 

Crude  liber--  _  3.93 

Ether  extract-.  .32 

and  the  animal  gained  0.17  pound  of  body  protein,  in  addition  to  that  stored 
in  the  wool,  and  a  small  amount  of  body  fat. 

In  a  series  of  20  digestion  and  metabolism  experiments  by  Schulze  and 
Marcker,3  decidedly  smaller  amounts  of  protein  proved  sufficient  to  maintain 
nitrogen  equilibrium.  In  one  case  on  a  ration  containing  as  little  as  0.335 
pound  digestible  crude  protein  per  1,000  pounds  live  weight,  but  having  a  very 
wide  nutritive  ratio  (1: 17.2)  there  was  a  slight  gain  of  total  protein,  but  one 
less  than  the  amount  required  for  the  growth  of  wool.  If  we  exclude  this 
experiment  and  also  4  experiments  in  which  it  is  evident  that  an  excess  of 
protein  was  fed,  we  have  as  the  average  of  6  experiments  in  which  no  loss  of 
body  protein  was  observed  O.G53  pound  digestible  crude  protein  per  1,000 
pounds  live  weight,  while  in  two  other  experiments  in  which  the  minimum 
losses  of  0.005  and  0.015  pound  body  protein  were  observed,  the  protein  supply 
was,  resi>ectively,  O.G55  and  0.690  pound.  It  is  evident,  then,  that  the  protein 
supply  of  the  sheep  can  be  materially  reduced  below  the  amount  fed  in  Henne- 
berg  and  Stohmanu's  experiments  without  leading  to  a  loss  of  body  protein. 
That  such  is  the  case  seems  to  be  clearly  shown  by  the  recent  investigations 
of  Katayama  at  the  Moeckeru  Experiment  Station,*  in  which  increasing  amounts 
of  nearly  pure  protein  ("  aleuronat ")  were  added  to  a  basal  ration  very  poor 
in  protein,  consisting  of  hay,  oat  straw,  starch,  and  cane  sugar.  The  protein  in 
every  case  was  substituted  for  a  corresponding  amount  of  starch,  so  that  the 
total  energy  of  the  ration  remained  substantially  unchanged.  In  the  third 
I>eriod  of  the  experiment  both  of  the  two  sheep  showed  some  loss  of  body  pro- 
tein, while  in  the  fourth  period,  with  more  protein  in  the  food,  a  gain  was  noted. 
In  neither  case  was  the  growth  of  wool  taken  into  consideration.  P»y  adding  in 
the  one  case  the  loss  of  body  protein  to  the  digestible  protiMii  of  the  food  and 
in  the  other  period  subtracting  the  gain,  the  author  gets  the  following  comparison  : 

Prolfin  requirement  (>f  xJieeji  /n  r  dai/  nml  Iica*! — h~t!l<ii/<i>/ni. 


I     Sheep  I        Sheep  II 
( weight ,  34    ('weight .  :!«• 
kilograms),  kilograms). 


1 'priori  III: 

Xitrofjen  digested. . . 
Loss  of  body  protein. 


Period  IV: 

Nitrogen  digested 

(lain  of  bodv  nitrogen. 


Average  for  maintenance 


Maintenance  per  1.000  pounds  live  weipht: 
Nitrogen.. . 


Protein .379 


1  Neue  Roitril'jo,   etc. 

2  Estimated  by  Kellner  to  contain  1.04  pounds  of  true  protein. 

3  Wolff  :   Dio  Krnahruns  dcr  I.andwirtseliaftlichen  Nutztiere.  p.  .".OO. 

4  Die  Landwirtscliaftlichen  Versucli-Stationcn,  vol.  GO,  p.  "21. 


96  MAINTENANCE    RATIONS    OF   FAEM   ANIMALS. 

On  the  average  of  the  two  animals,  0.41  pound  digestible  crude  protein  per 
1.000  pounds  live  weight  was  apparently  sufficient  to  prevent  a  loss  of  nitrogen 
from  the  body.  The  crude  protein  in  this  case  was  practically  all  true  protein, 
only  minimum  amounts  of  nonprotein  being  present  in  the  ration.  Since,  how- 
ever, the  growth  of  wool  must  have  gone  on,  with  a  corresponding  storage  of 
nitrogen,  this  apparent  maintenance  ration  would  really  result  in  a  loss  of 
protein  by  the  active  tissues  of  the  body. 

If  we  add  to  Katayama's  average  0.14  pound  per  1,000  pounds 
live  weight  for  the  growth  of  wool,  we  get  0.55  pound  as  represent- 
ing the  minimum  protein  requirement  for  the  maintenance  of  mature 
sheep,  including  the  growth  of  wool.  It  is  interesting  to  note  that, 
according  to  these  figures,  the  actual  maintenance  requirement  for 
the  body  tissues  is  quite  as  low  relatively  as  for  cattle. 

It  is  true  that  some  earlier  experiments  seem  to  indicate  a  greater 
demand  for  protein  than  the  foregoing  figures  show.  Thus,  in 
the  experiments  cited  on  page  80  to  illustrate  the  influence  of  the 
protein  supply  upon  its  katabolism,  a  ration  containing  about  2.5 
pounds  digestible  protein  per  1,000  pounds  live  weight  seemed  to  be 
about  sufficient  for  maintenance,  including  the  wool  production, 
while  a  ration  containing  2.27  pounds  showed  a  loss  of  protein.  Simi- 
larly, in  earlier  experiments  by  Henneberg,  Fleischer,  and  Miiller,1 
a  ration  containing  1.25  pounds  digestible  crude  protein  following 
one  supplying  G.51  pounds  resulted  in  a  loss  of  protein  by  the  animal. 
Notwithstanding  these  isolated  results,  however,  it  seems  justifiable 
to  accept  the  lower  figure  obtained  by  Kata3Tama  as  representing  ap- 
proximately the  minimum  protein  requirement  of  mature  sheep. 


The  only  data  available  as  to  the  minimum  protein  requirement  of 
swine  are  derived  from  the  two  experiments  upon  fasting  animals  by 
Meissl.  Strohmer.  and  Lorenz  (referred  to  on  p.  51).  The  animals 
were  Yorkshire  swine,  one  14  months  old  and  weighing  140  kilograms, 
and  the  second,  whose  age  is  not  given,  weighing  120  kilograms.  In 
I  lie  fast  ing  slate  the  nitrogen  excretion  of  these  animals  was  as 
follows : 


Live 

weight. 

Nitrogen 
excretion. 

Kilns. 

140 

Grams. 
9.80 

120 

6.77 

Tlu-  nitrogen  excretion   was  equivalent,  respectively,  to  0.44  and 

»5   pi'iind   of  protein   per    1.000  pounds  live  weight,  or  about  the 

oiuiU    which    appear    to   be   required    for   cattle   and    sheep.     Xo 

:  .lnhivs!,,Tirl,l    (],  i-  . U'rirult  uivh.-inic.   vols.    10-17,    II,   p.   145. 


THE    OPTIMUM    OF    PROTEIN. 


97 


experiments  are  on  record  which  demonstrate  the  sufficiency  of  this 
amount  as  a  maintenance  ration. 


THK    IIORSK. 


In  the  experiments  by  Grandeau  and  Le  Clerc  described  on  pages 
(52-63  the  nitrogen  balance  of  the  horses  was  determined  during  6  of 
the  periods.  The  following  table  shows  the  amounts  of  protein  and 
of  nonprotein  nitrogen  digested  in  each  period,  the  urinary  nitrogen, 
ii nd  the  small  losses  in  epithelial  tissue  (epidermis,  hoofs,  hair,  etc.)  : 

Nitrogen  balance  of  horxcx — Clramlcau  and  Lr  C/rrr. 


Morse  No.  1.                        Horse  No.  2.                        Horse  No.  3. 

January, 

1884. 

April,  1884.  ^Ig)**' 

MO,.  ieti      December, 
May,  1884.          1(^.j 

March, 

1884. 

Digested: 
Protein  nitrogen              •   - 

Grams. 
43.19 
1.20 

Grams. 
34.29 
-  1.01 

Grams. 
38.94 
-  3.23 

Grams. 
34.22 
10.78 

Grams. 
41.82 
-  2.09 

Grams. 
24.72 

-  4.58 

Total  nitrogen 

44.39 

33.28 

35.71 

35.00 

39.73 

20.14 

Nitrogen  of  epithelial  tissue.  .  . 

1.46 
35.17 
7.76 

1.46 
38.75 
-  6.93 

1.46 
30.70 
3.55 

1.46 
41.92 
1.62 

1.46 
37.  02 
.65 

1.46 
32.70 
-14.02 

Nitrogen  gained 

Omitting  the  results  upon  horse  No.  3  in  March,  when  the  diges- 
tible protein  was  exceptionally  low,  the  other  five  periods  show  an 
average  daily  gain  of  nitrogen  of  1.33  grams,  while  the  average  crude 
protein  digested  (total  X.X6.25)  was  235  grams,  equivalent  to  0.59 
pound  per  1.000  pounds  live  weight. 

THE  OPTIMUM   OF   PROTEIN. 

The  data  of  the  foregoing  paragraphs  seem  to  indicate  a  striking 
uniformity  in  the  minimum  protein  requirement  of  the  principal  spe- 
cies of  domestic  animals  when  mature,  0.4  to  0.6  pound  per  1,000 
pounds  live  weight  apparently  sufficing  to  maintain  nitrogen  equilib- 
rium under  favorable  conditions. 

It  should  be  clearly  understood,  however,  that  this  figure  repre- 
sents a  more  or  less  accurately  determined  limit.  It  purports  to  be 
the  amount  below  which  the  protein  supply  can  not  be  reduced 
without  eventual  protein  starvation.  The  animal  body,  however, 
may  adjust  itself  to  a  wide  range  of  protein  supply  above  the  mini- 
mum, using  some  of  it  to  increase  the  stock  of  protein  in  the  body 
and  katabolizing  the  remainder  as  fuel  material.  An  increase  in  the 
protein  supply  above  the  minimum  results,  after  a  relatively  short 
time,  in  the  maintenance  of  the  body  protein  at  a  higher  level.  The 
practical  question  in  actual  maintenance  is  far  less  in  regard  to  the 
8481)°— Rull.  143—12 7 


98  MAINTENANCE    RATIONS    OF    FARM    ANIMALS. 

least  amount  of  protein  which  may  be  used  than  as  to  the  most  ad- 
vantageous level  of  protein  nutrition;  that  is,  as  to  the  optimum  of 
protein. 

This  question  has  been  warmly  debated  in  connection  with  human 
nutrition. 

Numerous  recent  investigations,  notably  those  by  Chittenden  and  his  asso- 
ciates,1 have  shown  that  the  protein  of  human  dietaries  can  be  reduced  much 
below  the  amount  previously  regarded  as  necessary.  In  most  cases  there  is  no 
possibility  of  a  direct  comparison  with  the  fasting  katabolism  of  the  same  indi- 
vidual, but  as  previously  stated  (p.  77)  a  considerable  number  of  instances  are 
on  record  in  which  the  nitrogen  supply  has  been  reduced  to  an  amount  mate- 
rially lower  than  that  usually  found  for  the  fasting  protein  katabolism  of 
individuals  of  the  same  weight  without  leading  to  a  loss  of  protein  from  the 
body.  In  all  these  experiments,  the  nonuitrogenous  nutrients  consisted,  as  is 
usually  the  case  in  human  dietaries,  to  a  considerable  extent  of  carbohydrates. 

Moreover,  while  some  of  the  earlier  experiments  were  for  short  periods  and 
on  comparatively  few  individuals,  Chittenden's  investigations  covered  long 
periods  and  were  made  on  26  different  individuals,  including  5  professional  men 
under  observation  for  8  months,  13  soldiers  observed  for  G  months, 
and  8  trained  athletes  under  observation  for  5  months.  His  results  clearly 
demonstrate  the  possibility  of  maintaining  the  body  protein  and  fully  preserv- 
ing the  health  and  vigor  upon  a  low  protein  diet.  In  other  words,  a  relatively 
low  level  of  protein  nutrition  for  several  months  is  not  inconsistent  with  health 
and  efficiency. 

In  some  of  the  earlier  experiments  in  which  very  low  protein  diets  were  fed 
to  dogs,  the  health  of  the  animals  suffered  seriously  and  there  has  been  a 
tendency  to  ascribe  these  ill  effects  to  the  continued  use  of  very  small  amounts 
of  protein.  Later  investigations  by  Chittenden,  however,  in  which  dogs  were 
kept  on  a  low  protein  diet  for  the  greater  part  of  a  year,  seem  to  have  demon- 
strated that  the  ill  effects  observed  in  the  earlier  experiments  were  due  to  un- 
hygienic conditions  and  not  to  the  low  protein  diet.  It  may  be  remarked  that  in 
experiments  upon  cattle,  rations  very  low  in  protein  have  been  fed  for  a  con- 
siderable time  without  any  perceptible  deleterious  effects.  No  similar  determi- 
nations upon  other  species  of  farm  animals  appear  to  have  been  made. 

On  the  whole,  then,  it  can  not  be  said  that  a  considerable  surplus  of 
protein  over  the  minimum  requirement  for  maintenance — that  is,  the 
maintenance  of  protein  nutrition  on  a  high  plane — has  been  proved 
to  be  of  any  material  advantage  in  the  maintenance  either  of  men  or 
domestic  animals  during  periods  covering  several  months.  Whether 
a  continued  low  protein  diet  through  years  or  generations  would 
show  a  different  result  is  at  present  largely  a  matter  of  speculation. 
It  is  to  be  remarked,  however,  that  the  particular  point  under  dis- 
cussion is  the  protein  requirement  of  the  mature  organism.  That  a 
deficiency  of  protein  in  the  diet  of  a  growing  animal  may  have 
disastrous  results  is  clear.  If,  however,  the  habitual  food  supply 
of  a  race  of  men  or  a  group  of  animals  is  low  in  protein,  the  young 
are  likely  to  share  this  deficiency  with  the  mature,  and  it  seems  not 

1  Physiological  Economy  in  Nutrition.      Stokes  Co.,  1907. 


RELATIVE  VALUES  OF  PROTEINS.  99 

impossible  that  this  is  an  important  factor  in  the  alleged  physical 
inferiority  of  certain  races  of  men  living  on  a  low  protein  diet. 
This  consideration  warns  us  to  exercise  care  in  this  respect  in  the 
management  of  the  breeding  herd. 

In  the  actual  maintenance  feeding  of  farm  animals,  the  matter  of 
the  digestibility  of  the  ration  must  also  be  considered.  It  has  been 
shoAvn  that  a  relative  deficiency  of  protein  in  the  ration  tends  to 
depress  the  apparent  digestibility  of  both  the  protein  and  nonnitro- 
genous  nutrients,  especially  in  the  case  of  ruminants.  A  maintenance 
ration  for  these  animals  containing  the  minimum  amount  of  protein, 
together  writh  the  quantities  of  nonnitrogenous  nutrients  required  to 
maintain  the  energy  supply,  would  have  a  nutritive  ratio,  computed 
in  the  ordinary  wTay,  of  approximately  1 : 12.  On  such  a  ration,  there 
would,  in  all  probability,  be  some  loss  of  digestibility.  An  increase 
of  its  protein  by  50  per  cent  would  very  probably  effect  a  gain  in 
digestibility  which  would  more  than  offset  the  increased  cost,  if  any. 
Indeed,  unless  feeds  especially  poor  in  protein  are  used,  it  may  often 
be  difficult,  even  if  desirable,  to  reduce  the  protein  content  of  a  main- 
tenance ration  to  the  low  level  of  absolute  necessity. 

RELATIVE  VALUES  OF  PROTEINS. 

In  the  discussions  of  the  foregoing  paragraphs,  following  the  usual 
practice,  the  word  protein  has  been  used  as  if  it  designated  a  single 
chemical  individual.  In  reality,  of  course,  this  is  very  far  from 
being  the  case.  The  protein  of  the  body  or  of  the  feed  in  this  con- 
ventional sense  includes  a  large  number  of  distinct  and  in  some  re- 
spects, widely  differing  proteins.  The  studies  of  the  chemical  struc- 
ture of  the  protein  molecule  made  in  recent  years,  beginning  with  the 
fundamental  investigations  of  Emil  Fischer,  have  shown  marked  dif- 
ferences in  the  proportions  of  the  various  "building  stones''  (amino- 
acids,  etc.)  contained  in  different  proteins,  while  studies  in  immunity 
have  led  to  the  recognition  of  marked  specific  and  individual  bio- 
logical differences  in  animal  proteins,  although  these  have  not  been 
definitely  correlated  with  differences  of  chemical  constitution.  It  is 
pertinent  to  inquire,  therefore,  whether  we  are  justified  in  discussing 
the  nutritive  functions  of  feed  protein  as  a  group  or  whether  we  must 
consider  each  individual  protein  by  itself.  In  other  words,  are  there 
recognizable  differences  in  nutritive  value  between  individual  pro- 
teins ? 

DIFFKRENCKS    IN    CONSTITUTION    OF    PROTKINS. 

In  discussions  of  this  question,  the  chief  emphasis  has  been  laid 
upon  the  demonstrated  differences  in  the  proportions  of  the  various 
cleavage  products  yielded  by  the  different  proteins  when  subjected 


100 


MAINTENANCE    RATIONS    OF    FARM    ANIMALS. 


to  acid  hydrolysis.     The  following  table  shows  some  of  the  more 
recent  results  obtained  by  Abderhalden  and  by  Osborne : 

Constituents  of  proteins — AMerltahlen  and  Osborne. 


Constituents. 

G  Had  in 
of 
wheat.1 

Gluten- 
inof 
wheat.1 

Zein 
of 
maize.1 

Pha- 
seolin  of 
white 
bean.  ' 

Casein.  2 

Egg 
albu- 
min.2 

Serum 
albu- 
min of 
horse 
blood.  2 

Serum 
globu- 
lin of 
horse 
blood.  2 

Ox 
mus- 
cle.3 

Edestin 
from 
hemp.< 

Glycocol 

P.  ct. 

P.ct. 

0.  89 

P.ct. 

P.ct. 

0  55 

P.ct. 

0  00 

P.ct. 

0  00 

P.ct. 

0  0 

P.ct. 
3  5 

P.ct. 

2  06 

P.ct. 

3  80 

A  huiiu  .                  ... 

2.00 

4.65 

1.80 

.90 

2  10 

9  7 

2  2 

3  72 

3  60 

A  m  i  n  o  -  valerianic 
acid 

.21 

.24 

1  04 

1.00 

(i) 

81 

i'->\ 

Leuein                

5.61 

5.95 

9.56 

10.50 

6  10 

20  0 

18  7 

11  65 

20  90 

Prolin  

7.06 

«4.  23 

2.77 

3.10 

2.25 

1  1  0 

1  2  8 

5  S9 

8  1  70 

Phenylalanin 

2.35 

1.97 

3.25 

3  20 

4  40 

3  1 

3  8 

3  15 

9  40 

Aspartic  acid  

.58 

.91 

5.24 

1  20 

1  50 

3  1 

2  5 

4  51 

4  50 

Glutamic  acid 

37.33 

23  42 

16  87 

14  54 

11  00 

9  10 

8  5 

15  49 

7  f,   30 

Serin  

.13 

.74 

.38 

.23 

.6 

(?) 

33 

Tyrosin                 .  .   . 

1.20 

4.25 

2.17 

4  50 

1  10 

2  1 

o   - 

2  20 

2  10 

Cystin          

.45 

.02 

.06 

20 

2  3 

7 

25 

Lysin  

.00 

1.92 

.00 

3.59 

5.80 

7  59 

1  00 

Histidin  

.61 

1.76 

.81 

1.97 

2.59 

1.76 

1  10 

Arginin.        

3.16 

4.72 

1.82 

4.72 

4.84 

7  47 

11  70 

Ammonia  

5.11 

4.01 

3.61 

2.06 

1.95 

1.63 

1  07 

Trvptophan 

(5) 

(5) 

.00 

(5) 

1  50 

(S) 

(V) 

(•'') 

(5) 

n\ 

Total  

f«.  81 

."9.  60 

23.11 

53.64 

52.37 

28.38 

42.6 

45.2 

67  30 

1  Osborne.      The  proteins  of  the  wheat  kernel,  pp.   110,    113,   and   118. 

2  Abderhalden.      Lehrbuch  der  physiologischon  Chemie. 

3  Osborne.      The  American  Journal  of  Physiology,   vol.  24,   p.   437. 

4  Abderhalden.      Loc.  cit. 

5  Present. 

•  A  prolin. 

7  A  later  determination  by  Osborne  (American  Journal  of  Physiology,  vol.  15,  p.  333), 
confirmed  by  Abderhalden,  gave  18.74  per  cent. 

While  many  of  the  figures  of  the  foregoing  table  can  not  lay  claim  to  a  high 
degree  of  quantitative  accuracy,  it  is,  nevertheless,  clear  that  the  proportions 
of  the  various  atomic  groupings  in  the  protein  molecule  vary  within  wide 
limits,  while  in  some  cases  the  most  careful  search  has  failed  to  show  the 
presence  of  certain  constituents.  Thus,  glycocol  and  lysin  were  not  found  in 
gliadin,  nor  lysin  and  tryptophan  in  zein,  while  ox  muscle  yielded  a  consider- 
able percentage  of  lysin,  a  moderate  amount  of  glycocol,  and  showed  the  pres- 
ence of  tryptophan. 


ABSENCE   OF   CERTAIN    CONSTITUENTS. 

There  is  now  a  general  agreement  that  in  the  process  of  digestion  the  pro- 
teins of  the  feed  undergo  extensive  cleavage  and  are  to  a  large  extent  broken 
down  either  into  individual  amino-acids  or  into  comparatively  simple  peptid- 
like  compounds.  These  substances  are  resorbed  by  the  intestinal  epithelium 
and  the  diverse  proteins  of  the  body  are  formed  from  them  by  synthetic  proc- 
esses, either  in  the  intestinal  wall  or  beyond.  Such  being  the  case,  it  has 
seemed  clear  that,  for  example,  the  proteins  of  ox  muscle  containing  2.O>  per 
cent  of  glycocol  and  7.5J)  per  cent  lysin  could  not  be  produced  from  gliadin. 
which  is  lacking  in  both  those  groups,  nor  from  zein,  which  lacks  lysin  and 
tryptophan. 

The  classic  example  of  the  effects  of  such  a  deficiency  is,  of  course,  gelatin, 
which  contains  neither  tyrosin,  cystin,  nor  tryptophan.  Bischoff  and  Voit  * 


1  Hermann's  Iliindbncli  der  I'hyslologie,  vol.  G,  pp.  122  and  395. 


RELATIVE  VALUES  OF  PROTEINS.  101 

long  ago  showed  that  gelatin  in  whatever  amount  fed  is  completely  katabolized 
in  the  body,  at  least  so  far  as  its  nitrogen  is  concerned,  although  it  may  some- 
what diminish  the  waste  of  protein  tissue.  Subsequent  investigations  by  Kirch- 
maim  1  and  by  Krummaclier '  showed  that  when  gelatin  is  fed  alone  an  amount, 
equivalent  to  the  fasting  nitrogen  katabolism  may  reduce  the  loss  of  nitrogen 
from  the  body  by  something  over  20  per  cent,  while,  on  the  other  hand,  even 
very  large  quantities  can  effect  a  reduction  of  only  about  35  i»er  cent.  Murlin  * 
finds  that  in  the  mixed  diet  of  men  about  two-thirds  of  the  protein  may  be 
replaced  by  gelatin  without  disturbing  existing  nitrogen  equilibrium.  That  the 
inferior  value  of  gelatin  is  due  to  the  absence  of  certain  groupings  in  its  mole- 
cule seems  to  have  been  shown  by  Kaufmann,4  who  found  that  gelatin  with  the 
addition  of  proper  quantities  of  tyrosin,  cystin,  and  tryptoplian  was  able  to 
maintain  nitrogen  equilibrium  at  least  several  days. 

Investigations  by  Wilcock  and  Hopkins5  UJKIU  zein.  which,  as  already  noted, 
lacks  lysin  and  tryptophan,  approach  the  subject  from  a  slightly  different  angle. 
They  found  that  a  diet  containing  zein  as  its  only  protein  material  was  unable 
to  maintain  growth  in  young  mice.  The  addition  of  tryptophan  approximately 
doubled  the  survival  period  and  added  markedly  to  the  well-being  of  the  ani- 
mals, but  was  unable  to  maintain  life  indefinitely.  On  the  zein  diet  the  animals 
became  torpid  early  in  the  experiment  and  almost  comatose  before  death  en- 
sued, while  with  the  addition  of  tryptophan  no  such  symptoms  were  observed. 
The  authors  interpret  this  result  as  showing  that  tryptophan  has  some  specific 
function  in  the  body  aside  from  the  mere  maintenance  of  nitrogen  equilibrium. 
The  results  recently  obtained  by  Osborne  and  Mendel,"  however,  show  that 
great  caution  is  necessary  in  the  interpretation  of  such  survival  experiments, 
while  they  also  indicate  that  growth  is  largely  dependent  on  some  other  factor 
than  the  protein  supply. 

Plxperiments  on  rats  by  Henriques7  gave  a  similar  result  as  regards  zein. 
with  which  it  was  found  impossible  to  obtain  nitrogen  equilibrium  in  short 
experiments.  On  the  other  hand,  however,  an  abundant  supply  of  gliadin  main- 
tained nitrogen  equilibrium  for  some  days,  notwithstanding  the  fact  that  it 
lacks  both  lysin  and  glycocol. 

PROPORTIONS  OK  COX STITfKNTS. 

Still  further,  even  when  all  the  constituents  of  the  body  protein  are  present 
in  the  feed  protein,  their  proportions  may  be  widely  different.  Thus,  a  mixture 
of  equal  parts  of  gluteniu  and  gliadin  would  contain  about  30  per  cent  of  glu- 
tamic  acid  as  compared  with  about  half  that  amount  in  ox  muscle,  while  the 
latter  yields  over  11.5  per  cent  of  leucin  as  compared  with  less  than  6  per  cent 
from  the  former.  In  such  a  case  it  would  seem  that  the  tissues  in  which  the 
synthesis  takes  place  must  make  a  selection  from  the  material  supplied  by  the 
digestive  tract,  reproportioning  the  various  constituents,  while  the  excess  of  cer- 
tain  ones  would  be  attacked  by  the  deamidizing  enzynis  of  the  body,  their  nitro- 
gen being  finally  excreted  as  urea.  Accordingly,  it  might  be  anticipated  that  the 
more  nearly  the  feed  protein  resembled  in  its  make-up  the  average  of  the  body 


1  Zeitschrift  fiir  Wologie.   vol.  40.   p.  r>4. 
-Zeitschrift  fiir  Biologic  vol.   4U.  p.  J4J. 

3  American  Journal  of  Physiology,  vol.  10,  p.  -So  :  vol.  CO.  p.  :J.".4. 

4  Archiv  fiir  die  Gesamrnte  Physiologie  dcs  Menschen  und  <l<-r  Thiere  (Pfltigen.  vol.  109, 
.   440. 

5  Journal  of  Physiology   (London),  vol.  "5,  p.  SS. 
"Carnegie  Institute  of  Washington    Publication   No.   lf>6. 
7  Zeitschrift  fiir  Physiologische  C'hemie.  vol.  GO.  p.   105. 


102  MAINTENANCE   RATIONS    OF    FARM    ANIMALS. 

proteins  the  more  economically  it  could  be  utilized  for  the  building  up  or  repair 
of  protein  tissues,  and  that  thus  there  might  be  very  considerable  differences  in. 
nutritive  value  between  different  proteins. 

EXPERIMENTAL    METHODS. 

Considerations  like  the  foregoing  have  been  advanced  by  numerous  authors, 
but  as  yet  little  satisfactory  experimental  work  upon  the  relative  values  of  the 
proteins  has  been  reported.  Indeed  the  problem  is  far  from  being  an  easy  one. 
Aside  from  technical  difficulties,  it  is,  of  course,  a  simple  matter  to  substitute 
one  protein  for  another  in  the  ration ;  the  difficulty  lies  in  finding  a  satis- 
factory measure  of  the  effects.  The  most  obvious  thing,  of  course,  is  a  deter- 
mination of  the  balance  of  income  and  outgo  of  nitrogen,  which,  when  extended 
over  reasonably  long  periods,  affords  an  approximate  measure  of  the  relative 
gain  or  loss  of  protein.  As  has  been  clearly  shown  on  preceding  pages,  however, 
the  nitrogen  balance,  especially  in  a  mature  animal,  is  a  more  or  less  fluctuat- 
ing thing,  being  materially  affected  by  various  factors  besides  the  momentary 
protein  supply.  Especially  important  are  the  influence  of  the  previous  pro- 
tein supply  upon  the  general  level  of  protein  nutrition,  the  influence  of  the 
store  of  body  fat  carried  by  the  animal,  and  the  supply  of  available  energy 
in  the  feed.  Only  after  these  influences  have  been  eliminated  as  completely 
as  possible  can  differences  in  the  nitrogen  balance  be  ascribed  to  differences 
in  the  nature  of  the  proteins  consumed.  On  this  account,  experiments  in  which 
additions  of  protein  are  made  to  a  ration  already  containing  a  considerable 
supply  and  in  which  gains  of  nitrogen  in  different  periods  are  made  the  basis 
of  comparison  are  quite  unsatisfactory,  as  Magnus-Levy1  has  pointed  out. 
A  more  satisfactory  basis  of  comparison  is  the  amounts  of  the  different  pro- 
teins required  to  maintain  nitrogen  equilibrium  under  conditions  otherwise 
comparable.  Furthermore,  the  protein  supply  must  not  be  too  liberal.  Protein 
supplied  in  excess  of  the  minimum  requirement  is  utilized  largely  as  fuel  ma- 
terial. Under  such  circumstances,  it  is  easily  conceivable  that  proteins  differ- 
ing widely  in  constitution  may  furnish  enough  of  each  of  the  essential  cleavage 
products  to  meet  the  relatively  small  demand  for  the  maintenance  of  tissue  and 
that  thus  differences  really  existing  may  be  masked  by  the  excess  of  protein 
supplied. 

These  considerations  clearly  indicate  that  the  most  promising  method  of 
investigation  is  to  compare  the  minimum  amounts  of  the  different  proteins 
required,  along  with  an  abundance  of  nonnitrogenous  nutrients,  to  maintain 
nitrogen  equilibrium  on  as  low  a  plane  of  protein  nutrition  as  practicable  in 
Hie  same  animal  in  like  bodily  states  and  under  identical  conditions,  so  far 
as  it  is  possible  to  insure  these.  Any  consistent  differences  appearing  in  a 
considerable  number  of  trials  may  then,  it  would  seem,  be  safely  ascribed  to 
differences  in  the  nature  of  the  proteins. 

Thus  far  but  three  investigations,  according  to  the  general  method  just  out- 
lined, have  been  published,  all  of  them  appearing  within  the  year  1909.  For 
the  present  purpose  it  seems  superfluous  to  review  the  older  investigations, 
made  by  less  satisfactory  methods  and  in  many  cases  from  a  different  point 
of  view. 

MICHAUD'S   INVESTIGATIONS. 

Michaud2  experimented  on  three  dogs  by  substantially  the  method  just  out- 
lined. Reasoning  that  any  loss  in  transforming  feed  protein  into  body  protein 

'Von  Nonrdcn's  Ilamlbuch  o>r  Pathologic  dos  Sloffwcchsols,  vol.   1.  p.  7S. 
-  Xcitschrift  fiir  Physiolo.icisc-hc  Chcnu'o.  vol.  ".0.  p.  405. 


RELATIVE   VALUES    OF    PROTEINS.  103 

would  be  smaller  the  less  the  difference  in  the  constitution  of  the  two,  he  used 
as  his  standard  protein  supply  either  dog  flesh  or  the  ground  flesh  and  internal 
organs  (heart,  liver,  spleen,  and  testicles)  of  dogs.  This  material  may  be 
assumed  to  have  supplied  the  various  amino  acids,  etc.,  in  approximately  the 
proportions  required  to  maintain  the  protein  tissues  of  the  experimental  animals 
with  a  minimum  of  loss.  With  this  were  compared  gliadin  and  edestin  as  rep- 
resentatives of  the  vegetable  proteins  differing  quite  widely  from  those  of  the 
body  and  casein  as  an  animal  protein  more  or  less  similar  to  the  tissue  proteins. 

The  series  of  experiments  on  the  first  dog  affords  a  striking  illustration  of 
the  difficulties  in  the  way  of  successful  investigation  of  this  question.  After 
fasting  for  16  days  and  receiving  only  nonnitrogenous  feed1  (sugar  and  lard) 
for  28  days  more,  the  daily  nitrogen  excretion  (feces  and  urine)  was  reduced 
to  1.42  grams  per  day  and  appeared  to  have  become  approximately  constant. 
Quantities  of  the  various  protein  materials  containing  this  amount  of  nitrogen 
were  then  added  in  successive  periods  to  the  basal  nonnitrogenous  ration  and 
the  effect  upon  the  nitrogen  balance  determined,  the  periods  covering  from  6 
to  9  days  each.  In  three  periods  in  which  dog  flesh  was  fed,  the  animal 
gained  small  amounts  of  nitrogen  (0.08  to  0.17  gram  per  day)  ;  in  other  words, 
an  amount  of  protein  equal  to  the  fasting  katabolism  sufficed  to  produce  nitro- 
gen equilibrium.  Practically  the  same  result  was  also  attained  in  the  period 
in  which  "  Nutrose  "  (a  preparation  of  casein)  was  fed.  Three  periods  with 
gliadin,  on  the  contrary,  showed  in  every  case  a  loss  of  nitrogen  ranging  from 
0.33  to  0.52  gram  i>er  day ;  that  is,  the  gliadin  appeared  decidedly  less  valuable 
than  the  dog  flesh  or  casein  for  the  maintenance  of  the  body  protein.  Upon 
adding  more  gliadin  to  the  ration  it  was  found  necessary  to  increase  the  daily 
amount  to  the  equivalent  of  about  3.5  grams  of  nitrogen  before  nitrogen  equilib- 
rium was  reached. 

At  the  conclusion  of  this  series,  however,  two  3-day  periods  on  the  nitrogen- 
free  ration  (preceding  and  following  the  period  with  the  larger  amount  of 
gliadin)  showed  that  the  prolonged  feeding  on  rations  poor  in  protein  had  so 
lowered  the  plane  of  protein  nutrition  that  the  daily  fasting  katabolism  was 
now  equivalent  to  only  0.95  gram  of  nitrogen,  or  on  the  average  of  the  last 
two  days  of  each  period  to  only  0.82  gram.  In  other  words,  the  1.42  grams  of 
ihe  earlier  periods  did  not  represent  the  absolute  minimum  on  which  life 
could  be  maintained.  A  second  series  of  trials  was  therefore  instituted  in 
which  dog  tissue  was  compared  with  casein  and  edestin.  In  no  case  was 
nitrogen  equilibrium  quite  reached,  but  the  dog  flesh  still  showed  a  decided 
advantage  over  the  other  forms  of  protein.  The  dog,  however,  had  become 
very  much  reduced  and  died  during  the  final  period  on  dog  flesh,  the  autopsy 
showing  an  exceedingly  anemic  condition.  The  attempt  to  base  the  compari- 
sons of  the  different  proteins  upon  the  absolute  minimum  of  the  protein 
katabolism,  in  other  words,  involved  such  a  reduction  in  the  stock  of  body 
protein  and  consequently  such  an  abnormal  condition  of  the  animal  as  to  render 
the  value  of  the  results  questionable.  In  succeeding  experiments  on  two  other 
dogs,  therefore,  the  attempt  to  reach  the  absolute  minimum  of  the  protein 
katabolism  was  abandoned  and  the  amounts  of  the  several  proteins  added  to 
the  basal  nonnitrogenous  ration  were  either  made  equivalent  to  the  fasting 
katabolism  in  the  first  period  or  reduced  slightly  below  it  according  to  the 
judgment  of  the  experimenter.  The  results  were  in  accord  with  those  of  the 
first  series,  the  vegetable  proteins,  gliadin  and  edestin.  proving  notably  inferior 
to  the  dog  flesh  or  the  casein. 

1  No  mention  is  made  of  any  supply  of  ash  ingredients  other  than  those  contained  in 
the  various  forms  of  protein  used,  with  the  exception  of  a  small  amount  of  calcium  ear- 
lionnte  ip.  4-°>>. 


104 


MAINTENANCE    EATIONS    OF    FARM   ANIMALS. 


Upon  two  points,  however,  Michaud's  results  seein  open  to  question. 

First,  the  pure  proteins  which  he  employed,  as  well  as  the  sugar  and  lard, 
can  have  contained  but  minimal  amounts  of  ash,  while,  as  already  stated,  no 
mention  is  made  of  the  addition  of  any  ash  ingredients  except  calcium  car- 
bonate. In  those  periods,  then,  the  animal  was  apparently  in  a  state  of  par- 
tial or  entire  mineral  hunger.  The  dog  flesh  (or  in  two  periods  horse  flesh), 
on  the  other  hand,  contained  its  normal  amount  of  ash,  and  it  is  not  im- 
possible that  this  was  an  important  factor  in  determining  its  higher  value, 
although  it  must  be  admitted  that  this  explanation  does  not  apply  to  the 
casein  periods.  Second,  dog  tissue  or  horse  flesh  is  by  no  means  pure  protein, 
but  in  addition  to  ash  constituents  contains  a  great  variety  of  organic  com- 
pounds, which  may  have  been  quite  as  important  as  the  protein.  In  other 
words,  the  periods  on  tissue  are  not  comparable  with  those  on  pure  proteins. 

ZISTERER'S  EXPERIMENTS. 


Zisterer *  has  reported  two  series  of  similar  experiments,  also  on  a  dog. 
They  differed  from  Michaud's,  however,  in  that  the  periods  were  shorter  and 
that  each  feeding  period  was  interpolated  between  two  periods  on  a  nonnitro- 
genous  basal  ration  from  the  average  results  of  which  the  fasting  protein 
katabolism  of  the  animal  for  that  particular  bodily  condition  was  computed. 
Zisterer  experimented  with  casein,  wheat  gluten,  and  lean  meat  extracted 
with  water  (muscle  protein).  He  added  to  his  rations  the  chlorids  of  sodium, 
potassium,  and  calcium,  but  no  other  ash  ingredients.  The  ash  content  of 
the  feeds  was  small.  The  energy  supply  in  the  feed  was  in  every  instance 
ample  to  supply  the  needs  of  the  animal  as  computed  according  to  E.  Voit.2 
Taking  the  first  period,  on  casein,  as^an  example,  the  preliminary  period  on 
nitrogen-free  feed  covered  five  days  and  the  one  following  the  feeding  period 
four  days.  On  the  average  of  the  last  two  days  of  these  periods,  the  fasting 
protein  katabolism  was  equivalent  to  1.975  grams  nitrogen  daily.  During  the 
intermediate  4-day  period,  casein  containing  2.018  grams  nitrogen  per  day 
was  fed  and  the  average  daily  nitrogen  excretion  for  the  last  two  days  was 
found  to  be  2.333  grams.  Two  series  of  trials  of  this  sort,  made  in  inverse 
order,  yielded  the  following  results : 

Protein  metabolism  of  a  dog — Zisterer. 


Fasting 
nitrogen 
katabolism. 

Feed 
nitrogen. 

Total 
nitrogen 
excretion. 

Gain  of 
nitrogen 
by  animal. 

Series  I: 
Casein                                         

Grams. 
1.975 

Grams. 
2.018 

Grams. 
2.333 

Grams. 
—0.315 

2.125 

2.  021 

2  310 

294 

Wheat  gluten                             

1.951 

2.  017 

2.113 

—  .  0;Mj 

Series  II: 
Wheat  gluten 

1.800 

2.111 

2.  270 

—  .  1(>5 

Muscle  protein            

.806 

2.110 

1.903 

+  .207 

Casein  

.708 

2.108 

2.050 

+  .058 

A  verage: 
Casein...           

.842 

2.003 

2.  192 

-  .129 

Muscle  protein 

.  966 

2.  000 

2.109 

+   .043 

Wheat  gluten  

.870 

2.064 

2.  195 

+  .  131 

If  we  represent  the  total  nitrogen  excretion  upon  the  muscle  protein  by  100, 
that  observed  with  the  other  proteins  was  as  follows: 


1  Zeitschrlft  fiir  I?iolof,'i<>,  vol.  M,  p.   1.". 


-41.  p.   1 1::. 


RELATIVE  VALUES   OF   PROTEINS. 
Relative  nitrogen  excretion  <m  different  protein*. 


105 


Series  I. 

Series  II. 

Average. 

Casein  ....          .  .          .   . 

101 

108 

104 

Muscle  protein  

100 

100 

100 

Wheut  gluten  . 

91 

120 

104 

Compared  iu  this  way,  the  differences  disclosed  between  the  different  pro- 
teins are  small  iu  themselves,  and,  especially  in  the  case  of  the  wheat  gluten, 
are  discordant  in  the  two  series.  Apparently  the  differences  are  less  than  those 
which  may  be  plausibly  ascribed  to  variations  iu  the  conditions  of  the  several 
experiments.  The  latter  may  be  to  some  degree  eliminated  by  comparing  the 
total  nitrogen  excretion  with  the  fasting  nitrogen  katabolism  of  the  corre- 
sponding periods.  If  the  latter  be  represented  by  100,  the  relative  nitrogen 
excretion  on  the  several  proteins  was  as  follows : 


Series  I. 

Series  II.   | 

Average. 

Casein 

118.1 

120  0 

119  1 

Muscle  protein  . 

109.  0 

105.4 

107  2 

Wheat  gluten 

108  3 

126  5  1 

117  4 

This  second  method  of  comparison  seems  to  indicate  a  distinct,  although 
small,  inferiority  of  the  casein  as  compared  with  the  muscle  protein.  The 
same  is  true  of  the  average  result  with  wheat  gluten,  but  not  of  the  results 
of  the  individual  series.  Entirely  similar  results  are  obtained  if  the  calcula- 
tion is  made  only  upon  the  protein  nitrogen  of  the  feed  and  excreta  instead  of 
the  total  nitrogen.  Zisterer's  results  are,  of  course,  open  to  the  same  criticism 
made  on  Midland's,  viz,  that  the  so-called  muscle  protein  was  not  comparable 
with  the  pure  proteins  used  in  the  other  i>eriods. 

RESULTS    ARE    QUALITATIVE. 

Both  Michaud's  and  Zisterer's  results  are  in  a  sense  qualitative.  They  show 
that  certain  foreign  proteins  when  substituted  for  tissue  caused  a  relatively 
greater  nitrogen  excretion  and  were  therefore  less  efficient  in  maintaining  the 
nitrogen  balance  of  the  body.  For  gliadin  and  edestin,  Michaud  observed  a  nota- 
bly greater  difference  than  did  Zisterer  for  wheat  gluten.  For  casein  their  results 
are  quite  similar.  In  no  case  was  the  amount  of  foreign  protein  required  to 
reach  nitrogen  equilibrium  determined,  with  the  exception  of  one  short  period 
upon  gliadin  in  Michaud's  experiments.  In  both  cases,  the  differences  appear 
relatively  small.  On  the  basis  of  average  figures  for  the  proportions  of  four  of 
the  principal  amino-acids  in  the  different  proteins.  Zisterer  computes  much 
greater  possible  differences.  Representing  the  amount  of  muscle  protein  re- 
quired to  furnish  a  given  amount  of  each  one  of  the  four  amino-acids  by  100. 
Zisterer  calculates  that  .the  following  amounts  of  casein  and  of  wheat  gluten 
would  be  required  for  the  same  purpose: 


Muscle 
protein. 

Casein. 

Wheat 
glunn. 

To  furnish  equal  amounts  of: 
Alanin 

100 

444 

•>(}7 

Leucin 

100 

74 

154 

Glutamic  acid  

100 

124 

49 

TV  rosin 

100 

47 

102 

106  MAINTENANCE    RATIONS    OF    FARM    ANIMALS. 

As  was-  noted  above,  the  ash  supply  was  but  partially  considered  in  Zisterer's 
experiments,  no  mention  being  made  of  the  addition  of  ash  ingredients  with  the 
exception  of  sodium,  potassium,  and  calcium.  It  seems  not  impossible  that  the 
phosphorus  compounds  of  the  muscle  protein  may  have  had  something  to  do 
with  its  apparently  greater  availability. 

THOMAS'S  EXPERIMENTS. 

Thomas 1  has  attempted  to  determine  the  relative  values  of  the  mixed  proteins 
of  different  foods  by  a  method  differing  somewhat  from  that  employed  in  the 
two  foregoing  investigations.  As  has  been  shown  in  previous  pages,  on  an 
abundant  nonnitrogenous  ration,  especially  of  carbohydrates,  the  protein 
katabolism  of  the  body  may  be  reduced  to  a  very  low  limit  which  represents 
more  or  less  exactly  the  minimum  amount  of  protein  necessarily  broken  down 
in  the  vital  activities.  If  a  small  amount  of  protein  be  added  to  such  a  non- 
nitrogenous  ration,  it  will  tend  to  be  used  to  replace  body  protein,  since  the 
surplus  of  nonnitrogenous  material  tends  to  prevent  its  being  katabolized  to 
furnish  energy.  The  extent,  then,  to  which  any  given  protein  under  these  con- 
ditions diminishes  the  loss  of  protein  from  the  body  may  be  taken  as  the 
measure  of  its  maintenance  value.  The  principle  of  the  method  may  be  illus- 
trated by  the  following  supposititious  case. 


On  protein-:  On  protein 


free  food. 


food. 


Protein  digested 

Protein  katabolized 

Loss  of  protein  from  body. 


In  this  case,  four  parts  of  food  protein  obviously  replace  three  parts  of  body 
protein  and  the  percentage  availability  of  the  former  is  therefore  75.  The 
principle  of  the  method  is  similar  to  that  of  the  determination  of  the  percentage 
availability  of  energy  (p.  27). 

It  is  to  be  remarked  concerning  this  method,  first,  that  it  assumes  that  the 
percentage  availability  of  the  food  protein  is  the  same  for  all  amounts  below 
the  maintenance  requirement ;  in  other  words,  that  it  is  a  linear  function. 
This  is  an  unproved  assumption,  and  in  view  of  the  readiness  with  which 
protein  or  its  cleavage  products  in  the  body  seem  to  be  deamidized  and  utilized 
as  fuel,  the  assumption  seems  of  questionable  validity. 

Second,  in  applying  the  method  it  is  necessary  to  know  accurately  the  mini- 
mum amount  of  protein  katabolized  on  a  nitrogen-free  diet,  since  any  error  in 
the  determination  of  its  quantity  seriously  affects  the  final  result.  The  protein 
katabolism.  however,  under  these  conditions,  is  not  a  constant  quantity,  as 
has  already  been  pointed  out.  but  varies  more  or  less,  especially  with  the  state 
of  protein  nutrition  of  the  cells.  Accordingly,  it  must  be  determined  as  accu- 
rately as  possible  for  the  subject  at  the  time  of  the  experiment,  preferably 
immediately  before  and  immediately  after. 

Third,  the  amount  of  protein  fed  must  be  less  than  that  katabolized  on  the 
nitrogen-free  diet.  If  an  excess  of  protein  be  consumed,  the  additional  amount 
will  tend  to  be  katabolized  and  used  as  fuel,  thus  rendering  the  comparison 
between  the  two  periods  illusory,  since  it  is  obvious  that  any  such  oxidation 
of  protein  would  tend  to  make  its  availability  appear  too  low.  Thomas's 
experiments  were  made  upon  himself  and  included  four  series,  two  in  May  to 

1  Archiv  fiir  (Anatomic  unrt)   Pliysioloj,'io.  1909,  p.  219. 


RELATIVE  VALUES  OF  PROTEINS. 


107 


July  and  two  in  September  to  November  of  the  same  year.  He  determined  his 
protein  katabolism  upon  a  nonnitrogenous  diet  (chiefly  carbohydrates)  in  three 
or  four  day  periods  in  each  series  and  also  interpolated  single  nitrogen-free 
days  during  each  series.  The  results  of  these  periods  were  more  or  less  vari- 
able, but  the  final  values  employed  by  him,  although  representing  to  some  de- 
gree an  arbitrary  selection  of  days,  seem,  on  the  whole,  to  fairly  represent  the 
nitrogen  katabolism;  that  is,  they  satisfy  the  second  of  the  two  conditions 
above  pointed  out. 

With  these  values  for  the  protein  katabolism  were  compared  the  nitrogen 
balances  of  periods  of  from  two  to  four  days  (or  in  a  few  cases  only  one  day) 
in  which  single  foods  were  consumed  along  with  sufficient  carbohydrates  and 
fat  to  fully  supply  the  demands  of  the  body  for  energy.  The  technic  of  these 
periods,  however,  can  hardly  be  regarded  as  entirely  satisfactory.  Out  of  33 
days,  the  results  of  which  are  contained  in  his  final  table,  the  protein  digested 
was  greater  than  the  average  protein  katabolism  on  the  nitrogen-free  days  in 
21  cases,  the  difference  sometimes  being  considerable  and  sometimes  relatively 
insignificant.  As  already  pointed  out,  this  tended  to  make  the  availability 
appear  too  low,  and  it  is  noteworthy  that  the  excess  of  food  protein  is  especially 
large  in  the  experiments  upon  wheat  flour  which  show  a  strikingly  low  avail- 
ability. On  the  other  hand,  however,  it  is  also  true  that  a  very  low  availability 
was  found  for  maize  protein  in  experiments  in  which  but  a  slight  excess  was 
fed.  In  these  experiments,  however,  the  apparent  digestibility  of  the  protein 
was  remarkably  low.  ranging  from  56  to  GO  per  cent,  but  a  similar  low  digesti- 
bility (about  68  per  cent)  was  found  in  the  trials  with  rice.  Furthermore,  the 
periods  were  relatively  short  and  in  many  instances  the  nitrogen  intake  varied 
considerably  within  the  period,  so  that  it  may  be  questioned  whether  the  nitro- 
gen excretion  reached  a  stable  value.  Moreover,  to  some  extent  there  was  a 
more  or  less  arbitrary  selection  of  days  to  be  compared.  For  all  these  reasons 
Thomas's  results  must  be  accepted  with  more  or  less  reserve. 

His  final  results  for  the  percentage  availability  of  the  protein  of  different 
materials  are  as  follows,  the  results  being  calculated  in  three  different 
ways,  viz : 

A.  Fecal  nitrogen  all  regarded  as  derived  from  the  food,  that  is,  the  compari- 
son is  made  upon  the  basis  of  the  apparently  digested  protein. 

B.  Fecal   nitrogen   regarded   as  being  all   present   in  the  form  of  metabolic 
products. 

C.  One  gram  of  fecal  nitrogen  is  regarded  as  derived  from  metabolic  products 
and  the  remainder  from  undigested  food. 

Relative  availability  of  proteins — Thomas. 


<    104.  94 

103.  75 

Lean  beef  

Milk 

99.05 

99.71 

[     103.  09 

102.06 

Fish 

{      85.73 

89.37 

1      88.17 

91.95 

Rice 

/      83.00 

88.  .53 

87.09 

Crabs 

\      80.  26 
1      72.  GO 

90.73 

78.85 

89.  o5 

Yeast 

\      73.  38 
/      56.  63 

79.45 
73.48 

09.  58 

Casein  

\      53.40 
66.  69 

70.35 
70.14 

71.45 
67.  12 

Nutrose    . 

63  45 

69  02 

29  17 

36  25 

36.70 

43.04 

Wheat  flour  

04.  50 

42.04 

41.35 

27.  74 

51.10 

39.  75 

4v  97 
00.  94 

108  MAINTENANCE    RATIONS    OF    FARM    ANIMALS. 

Relative  availability  of  proteins — Thomas — Continued. 


B. 


c. 


| 

56.37 

G8.  80 

64.50 

72.67 

73.00 

:          78.  72 

80.33 
77.04 

83.18  !  
!          70.22 

78.66 

77.  45 

Cauliflower 

1      80.68 

1          87.  78 

Spinanh 

\      77.  62 
64.  50 

'          83.  88 
63.83 

Peas. 

i      49.  58 

59.89            55.15 

Cherries  .... 

\      51.64 
66.42 

59.  89            56.  01 

78.57 

f      24.  55 

40.47 

Maize  . 

\      12.25 

29.52 

.'            3.  54 

In  Zisterer's  experiments,  summarized  on  page  104,  the  feed  nitrogen  is 
so  slightly  in  excess  of  the  fasting  nitrogen  katabolism  that  it  would  seem  that 
no  large  error  would  result  from  applying  Thomas's  method  of  computation. 
The  results  are  as  follows : 

Percentage  availability. 


Series  I. 


Series  II.    !    Average. 


Casein 

82.26 

83.  77 

S3.  02 

Muscle  protein 

90.60 

95.40 

93.00 

Wheat  gluten  . 

91.97 

77.45 

84.71 

The  results  as  thus  computed  are  not  widely  different  from  those  obtained 
by  Thomas  for  casein  and  meat  protein,  but  are  slightly  higher  than  his  results 
for  wheat  protein.  Midland's  results  do  not  lend  themselves  to  computation  in 
this  way. 

Another  recent  investigation  of  a  different  character  may  be  mentioned  for 
the  sake  of  completeness,  viz,  that  on  frogs  by  Busquet,1  who  compared  lean 
veal  and  mutton  with  frog  meat  as  regards  the  amount  required  to  maintain 
the  live  weight  or  to  produce  a  unit  of  gain  of  weight  in  previously  fasting 
frogs.  In  this  respect  the  veal  and  mutton  were  found  distinctly  inferior  to  the 
frog  meat  per  unit  of  dry  matter. 

SIGNIFICANCE    OF    RESULTS. 

In  the  comments  upon  the  individual  experiments,  it  has  already 
been  clearly  indicated  that  they  are  open  to  criticism  in  many  re- 
spects, such  as  the  noncomparable  nature  of  the  protein  supply,  the 
lack  of  due  consideration  of  the  supply  of  mineral  matter,  etc. 
Moreover,  nearly  all  the  experiments  were  of  relatively  short 
duration. 

Taking  the  results  at  their  face  value,  however,  they  seem  to  in- 
dicate distinct  differences  in  the  nutritive  values  of  proteins.  The 
entire  lack  of  certain  groups,  as  in  the  case  of  gelatin  and  zein, 


'.Journal  de  I'll?  siolo.nic  of  do  Patliolo^i.-  C;«5n«'>ralo.  vol.  11    p.  :>00. 


RELATIVE  VALUES   OF   PROTEINS.  109 

seems  to  render  impossible  a  complete  substitution  for  tissue  pro- 
tein, while  differences  in  the  proportions  of  the  different  ammo 
acids  apparently  result  in  differences  in  the  replacement  values  of 
the  proteins,  although  these  differences,  especially  in  the  experiments 
of  Michaud  and  Zisterer,  are  hardly  as  great  as  might  have  been 
expected.  What  now  can  be  said  regarding  the  probable  significance 
of  these  differences  for  the  ordinary  problems  of  nutrition  ? 

In  the  first  place,  it  is  to  be  remarked  that  both  man  and  animals 
consume  a  mixture  of  proteins.  The  meat  eater  gets,  along  with 
his  gelatin,  the  various  muscle  proteins.  The  animal  fed  on  maize 
alone  receives  not  only  zein  but  its  associated  proteins,  amounting, 
according  to  Osborne,1  to  about  40  per  cent  of  the  total  protein  of 
the  grain,  whose  chemical  constitution  has  not  yet  been  reported. 
In  the  ordinary  mixed  rations  of  domestic  animals  it  would  appear 
that  there  must  be  a  considerable  degree  of  compensation  between 
the  different  proteins  as  regards  the  proportions  of  the  different 
cleavage  products  supplied  to  the  organism,  although  it  is  difficult 
to  judge  to  what  extent  this  is  the  case.  In  view,  however,  of  the 
rather  small  differences  observed  with  pure  proteins,  it  may  be 
questioned  whether  such  differences  as  exist  in  mixed  rations  are  of 
very  much  significance. 

In  the  second  place,  the  observed  differences  in  proteins  were  ob- 
tained in  experiments  in  which  small  amounts  of  protein  were  con- 
sumed and  in  which  the  animals  were  on  a  low  level  of  protein 
nutrition.  As  was  pointed  out  in  the  discussion  of  those  experiments, 
the  consumption  of  protein  in  excess  of  the  maintenance  requirement, 
such  as  usually  occurs  with  domestic  animals,  tends  to  obscure  the 
differences  between  the  proteins,  owing  to  the  considerable  extent  to 
which  protein  serves  for  fuel  purposes  under  those  conditions. 

Third,  almost  all  writers  upon  this  subject  tacitly  assume  the  in- 
ability of  the  body  to  change  one  amino-acid  into  another.  It  does 
not  appear  that  there  is  adequate  proof  of  this  inability.  Most  of 
the  amino  acids  concerned  belong  to  the  aliphatic  series  of  com- 
pounds, characterized  by  a  straight  carbon  chain,  and  as  between 
these  compounds,  at  least,  mutual  changes  are  not  difficult  to  conceive. 
As  a  matter  of  fact  one  such  change  appears  to  have  been  dem- 
onstrated. It  is  well  known  that  when  benzoic  acid  is  consumed  it 
is  paired  in  the  body  with  glycocol,  forming  hippuric  acid  which  is 
excreted.  It  seems  to  be  well  established  that  with  large  amounts  of 
benzoic  acid  more  combined  glycocol  may  appear  in  the  excreta  than 
can  be  assumed  to  have  been  present  as  such  in  the  amount  of  protein 
katabolized  during  the  same  time.  In  this  case,  apparently,  the  body 
is  able  to  manufacture  glycocol  from  some  other  substance,  pre- 

1  Journal  of  the  American  Chemical  Society,  vol.  19,  p.  532. 


110  MAINTENANCE    EATIONS    OF    FARM    ANIMALS. 

sumably  from  the  amino-acids  containing  a  larger  number  of  carbon 
atoms.  Whether  a  change  in  the  opposite  direction,  that  is,  a  syn- 
thetic change,  can  take  place  can  be  at  present  only  a  matter  of  specu- 
lation, but  such  a  change  would  be  entirely  analogous  to  the  building 
up  of  the  fatty-acid  chains  from  carbohydrates,  which  is  a  common 
occurrence  in  the  body.  Moreover,  Knoop,1  and  Embden  and 
Schmitz21  have  found  that  certain  ammo  acids  may  be  formed  syn- 
thetically from  the  corresponding  fatty  acids  and  ammonia,  thus 
indicating  a  possible  chemical  mechanism  by  which  a  deficient  sup- 
ply of  some  one  amino-acid  might  be  to  some  extent  overcome.  While, 
therefore,  we  can  hardly  suppose  that  the  proportions  of  the  different 
cleavage  products  is  a  matter  of  entire  indifference,  we  can  easily 
imagine  that  there  may  be  more  or  less  transformation  of  one  into 
another  in  case  of  need. 

Finally,  there  is  the  possibility  that  in  the  absence  of  some  one 
amino-acid  from  the  feed,  the  corresponding  acid  resulting  from  the 
katabolism  of  protein  tissue  may  to  a  greater  or  less  extent  escape  the 
action  of  the  deamidizing  enzyms  and  be  regenerated  to  protein. 
This  would  obviously  be  quite  in  accord  with  the  conception  of  the 
protein  metabolism  as  a  complex  of  reversible  enzym  reactions  which 
was  outlined  on  page  87. 

1  Zeitsclirift  fur  I'hysiologische  Chemic,  vol.  67,  p.  489. 

2  Biochemische  Zeitschrift,  vol.  29,  p.  423. 

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